Use tabular-nums font variant instead of switching to Tahoma for figures

Using a completely different font for figures leads to inconsistencies: https://github.com/ant-design/ant-design/issues/9422.
Most modern font systems defaults to [tabular figures](https://www.fonts.com/content/learning/fontology/level-3/numbers/proportional-vs-tabular-figures).
One exception to this is Apple's San Francisco which defaults to [proportional figures](http://martiancraft.com/blog/2015/10/san-francisco-part-2/#special-features-numerals).
There is, however, an official and clean way to switch to tabular figures. It's the [`font-variant` CSS property](https://developer.mozilla.org/en-US/docs/Web/CSS/font-variant-numeric) that can be set to `tabular-nums`.

This commit removes the "Monospaced Number" font altogether and use `font-variant: tabular-nums` instead where it was used.
It also moves closer to the sans-serif and monospace [system font stacks used by GitHub](http://markdotto.com/2018/02/07/github-system-fonts/).

components/date-picker/style/Picker.less

@@ -2,7 +2,7 @@
 
 .@{calendar-prefix-cls}-picker-container {
   .reset-component;
-  font-family: @font-family-no-number;
+  font-family: @font-family;
   position: absolute;
   z-index: @zindex-picker;
 

components/steps/style/index.less

@@ -66,7 +66,7 @@
     font-size: @font-size-lg;
     margin-right: 8px;
     transition: background-color .3s, border-color .3s;
-    font-family: @font-family-no-number;
+    font-family: @font-family;
 
     > .@{steps-prefix-cls}-icon {
       line-height: 1;

components/style/core/base.less

@@ -7,20 +7,6 @@
 //
 // Normalize is licensed MIT. https://github.com/necolas/normalize.css
 
-// http://stackoverflow.com/a/13611748/3040605
-@font-face {
-  font-family: "Monospaced Number";
-  src: local("Tahoma");
-  unicode-range: U+30-39;
-}
-
-@font-face {
-  font-family: "Monospaced Number";
-  font-weight: bold;
-  src: local("Tahoma-Bold");
-  unicode-range: U+30-39;
-}
-
 @font-face {
   font-family: "Chinese Quote";
   src: local("PingFang SC"), local("SimSun");
@@ -79,6 +65,7 @@ body {
   margin: 0; // 1
   font-family: @font-family;
   font-size: @font-size-base;
+  font-variant: tabular-nums;
   line-height: @line-height-base;
   color: @text-color;
   background-color: @body-background; // 2

components/style/mixins/reset.less

@@ -3,6 +3,7 @@
 .reset-component() {
   font-family: @font-family;
   font-size: @font-size-base;
+  font-variant: tabular-nums;
   line-height: @line-height-base;
   color: @text-color;
   box-sizing: border-box;

components/style/themes/default.less

@@ -34,9 +34,9 @@
 @body-background        : #fff;
 // Base background color for most components
 @component-background   : #fff;
-@font-family-no-number  : "Chinese Quote", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Helvetica, Arial, sans-serif;
-@font-family            : "Monospaced Number", @font-family-no-number;
-@code-family            : Consolas, Menlo, Courier, monospace;
+@font-family  : "Chinese Quote", -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Helvetica, Arial, sans-serif,
+"Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
+@code-family            : "SFMono-Regular", Consolas, "Liberation Mono", Menlo, Courier, monospace;
 @heading-color          : fade(#000, 85%);
 @text-color             : fade(#000, 65%);
 @text-color-secondary   : fade(#000, 45%);

components/time-picker/style/index.less

@@ -7,7 +7,7 @@
 
 .@{timepicker-prefix-cls}-panel {
   .reset-component;
-  font-family: @font-family-no-number;
+  font-family: @font-family;
   z-index: @zindex-picker;
   position: absolute;
 

docs/spec/font.en-US.md

@@ -22,16 +22,15 @@ While defining the font system for a visual system, we propose to start from the
 In order to implement a good font system, the first thing is to choose an appropriate font family. Ant Design prefers the system default font family and then also provides a set of alternative font libraries to maintain readability for screens on different platforms and browsers and to make sure it's always user friendly, stable and professional to end user.
 
 ```css
-font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
-             "Helvetica Neue", Helvetica, "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei",
-             SimSun, sans-serif;
+font-family: "Chinese Quote", -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC", "Hiragino Sans GB", "Microsoft YaHei", "Helvetica Neue", Helvetica, Arial, sans-serif,
+ "Apple Color Emoji", "Segoe UI Emoji", "Segoe UI Symbol";
 ```
 
-> References：https://www.smashingmagazine.com/2015/11/using-system-ui-fonts-practical-guide/
+> References：https://www.smashingmagazine.com/2015/11/using-system-ui-fonts-practical-guide/ and http://markdotto.com/2018/02/07/github-system-fonts/
 
-In addition, in a lot of applications, numbers often need to be displayed vertically. We set the numeric font to `Tahoma` specifically to make it a monospaced font.
+In addition, in a lot of applications, numbers often need to be displayed vertically. We set the CSS property `font-variant-numeric` to `tabular-nums;` to use [tabular figures](https://www.fonts.com/content/learning/fontology/level-3/numbers/proportional-vs-tabular-figures).
 
-> References：http://stackoverflow.com/questions/13611420/set-a-font-specifically-for-all-numbers-on-the-page
+> References：https://stackoverflow.com/questions/32660748/how-to-use-apples-new-san-francisco-font-on-a-webpage#comment78509178_32660790
 
 ## Base Font Size
 

site/theme/static/common.less

@@ -5,6 +5,7 @@ body {
 
 body {
   font-family: @font-family;
+  font-variant: tabular-nums;
   line-height: 1.5;
   color: @site-text-color;
   font-size: 14px;

site/theme/static/footer.less

@@ -51,6 +51,7 @@ footer {
     overflow: hidden;
     font-family: Avenir, @font-family;
     font-size: 16px;
+    font-variant: tabular-nums;
     a {
       color: rgba(255, 255, 255, 0.65);
       margin-left: 4px;

site/theme/static/header.less

@@ -93,6 +93,7 @@
   float: right;
   font-size: 14px;
   font-family: Lato, @font-family;
+  font-variant: tabular-nums;
   &.ant-menu-horizontal {
     border-bottom: none;
 

site/theme/static/home.less

@@ -8,6 +8,7 @@
   position: relative; // will-change: transform;
   color: @home-text-color;
   font-family: Avenir, @font-family;
+  font-variant: tabular-nums;
   .page {
     width: 100%;
     max-width: 1200px;
@@ -76,6 +77,7 @@
       margin: 8px 0 28px;
       letter-spacing: 0;
       font-family: Avenir, @font-family;
+      font-variant: tabular-nums;
     }
     p {
       font-size: 20px;
@@ -111,6 +113,7 @@
     text-decoration: none;
     border: 1px solid #2f54eb;
     font-family: @font-family;
+    font-variant: tabular-nums;
   }
 
   .banner-btn.components {

site/theme/static/markdown.less

@@ -24,6 +24,7 @@
   margin-top: 8px;
   font-family: Lato, @font-family;
   font-size: 30px;
+  font-variant: tabular-nums;
   line-height: 38px;
 
   .subtitle {
@@ -43,6 +44,7 @@
 .markdown h6 {
   color: @site-heading-color;
   font-family: Lato, @font-family;
+  font-variant: tabular-nums;
   margin: 1.6em 0 0.6em;
   font-weight: 500;
   clear: both;