feat: expose coercion and collections docs (#994)

Exposes the docs for `cdk/coercion` and `cdk/collections`.

Fixes angular/components#19530.
Fixes angular/components#18818.

Author: crisbeto

src/app/shared/documentation-items/documentation-items.ts

@@ -398,6 +398,22 @@ const DOCS: { [key: string]: DocItem[] } = {
         prefix: 'cdk-clipboard-',
       },
     },
+    {
+      id: 'coercion',
+      name: 'Coercion',
+      summary: 'Utility functions for coercing @Input into specific types.',
+      exampleSpecs: {
+        prefix: 'cdk-coercion-',
+      },
+    },
+    {
+      id: 'collections',
+      name: 'Collections',
+      summary: 'Utilities for managing collections.',
+      exampleSpecs: {
+        prefix: 'cdk-collections-',
+      },
+    },
     {
       id: 'drag-drop',
       name: 'Drag and Drop',