docs(docs-infra): Fixes the visibility of the copy link button in API documentation headings

Fixes the visibility of the copy link button in API documentation headings.
The button now appears on hover, improving the user experience.

(cherry picked from commit 15e3407dab)

adev/shared-docs/pipeline/api-gen/rendering/templates/section-heading.tsx

@@ -17,7 +17,7 @@ export function SectionHeading(props: {name: string}) {
 
   return (
     <h2 id={id} class={SECTION_HEADING}>
-      <a href={'#' + id} aria-label={label} tabIndex={-1}>
+      <a class="docs-anchor" href={'#' + id} aria-label={label} tabIndex={-1}>
         {props.name}
       </a>
     </h2>

adev/shared-docs/styles/_reference.scss

@@ -73,6 +73,20 @@
     }
   }
 
+  .docs-api {
+    h1,
+    h2,
+    h3,
+    h4,
+    h5,
+    h6 {
+      // Show copy link button when hovering the heading
+      &:hover docs-copy-link-button {
+        opacity: 1;
+      }
+    }
+  }
+
   .docs-reference-members {
     box-sizing: border-box;
     width: 100%;