fix(tabs): update min-width to follow the spec

- previous commits removed use of `getMinTabWidth` but never updated the related CSS
  - this applies the proper `min-width` CSS to match the spec
  - which is `72px` on `xs` and `160px` on everything else
- this also changes the left and right padding from `24px` to `12px` to align with the spec

Relates to #10406. Relates to #11432.

BREAKING CHANGE: Tab items now have a `min-width` and `padding` which matches the Material Design specification. For width, this is `72px` on `xs` screens and `160px` on all other screens. For left and right `padding`, this is now `12px` instead of `24px`. If your app needs to have tabs which are smaller than the spec, you will need to override `md-tab-item`'s `min-width` and `md-tab`'s `padding` styles.

Author: Splaktar

src/components/tabs/tabs.scss

@@ -172,6 +172,14 @@ md-pagination-wrapper {
     position: relative;
     justify-content: center;
   }
+  md-tab-item {
+    min-width: 72px;
+  }
+  @media (min-width: $layout-breakpoint-xs) {
+    md-tab-item {
+      min-width: 160px;
+    }
+  }
 }
 
 md-tabs-content-wrapper {
@@ -259,7 +267,7 @@ md-tab {
   font-size: 14px;
   text-align: center;
   line-height: $tabs-header-height - 24;
-  padding: 12px 24px;
+  padding: 12px;
   transition: background-color 0.35s $swift-ease-in-out-timing-function;
   cursor: pointer;
   white-space: nowrap;