build(aio): split the description property in API docs (#22401)

* The first paragraph is now split off into the `shortDescription` property.
* Usage of `howToUse` and `whatItDoes` have been updated.
* The "Overview" heading for class is removed as it is self-evident
* The original horizontal rule styling below the main heading is removed as not part of the new design

Closes #22385

PR Close #22401

aio/src/styles/2-modules/_banner.scss

@@ -1,25 +0,0 @@
-/* BANNER */
-
-.info-banner {
-    margin: 16px 0;
-    justify-content: center;
-    background: $white;
-    border: 1px solid rgba($lightgray, 0.5);
-    border-radius: 4px;
-    box-sizing: border-box;
-    padding: 16px;
-    background: $white;
-    height: auto;
-    overflow: visible;
-
-    @media screen and (max-width: 600px) {
-        text-align: center;
-    }
-
-    p, .text-body {
-        color: $darkgray;
-        line-height: 32px;
-        margin: 0;
-        text-align: center;
-    }
-}

aio/src/styles/2-modules/_modules-dir.scss

@@ -5,7 +5,6 @@
    @import 'alert';
    @import 'api-pages';
    @import 'api-list';
-   @import 'banner';
    @import 'buttons';
    @import 'callout';
    @import 'card';