Form: Add theme token (#16699)

* add form label size token

* add form label size token

packages/theme-chalk/src/common/var.scss

@@ -939,6 +939,11 @@ $--calendar-border: $--table-border !default;
 $--calendar-selected-background-color: #F2F8FE !default;
 $--calendar-cell-width: 85px !default;
 
+/* Form
+-------------------------- */
+/// fontSize||Font|1
+$--form-label-font-size: $--font-size-base !default;
+
 /* Avatar
 --------------------------*/
 /// color||Color|0

packages/theme-chalk/src/form.scss

@@ -96,7 +96,7 @@
     text-align: right;
     vertical-align: middle;
     float: left;
-    font-size: 14px;
+    font-size: $--form-label-font-size;
     color: $--color-text-regular;
     line-height: 40px;
     padding: 0 12px 0 0;