Updates the Angular UI Extensions overview doc to cover two new ExtensibleTableComponent features introduced in #22587 and #23670.

Multiple Selection (selectable / selectionType)

• [selectable]="true" enables a selection column
• [selectionType]="'single'" → radio buttons, no "select all" header
• Other types ('multiClick', 'checkbox', etc.) → checkboxes + "select all" header
• New inputs: selectable, selectionType, selected; new output: selectionChange

Infinite Scroll (infiniteScroll / loadMore)

• [infiniteScroll]="true" replaces pagination with scroll-triggered loading
• Emits (loadMore) when user scrolls within scrollThreshold px of the bottom; suppressed while [isLoading]="true"
• [tableHeight] sets a fixed px height for the scrollable viewport
• New inputs: infiniteScroll, isLoading, tableHeight, scrollThreshold; new output: loadMore

<abp-extensible-table
  [data]="items"
  [recordsTotal]="totalCount"
  [list]="list"
  [infiniteScroll]="true"
  [isLoading]="isLoading"
  [tableHeight]="500"
  (loadMore)="onLoadMore()"
/>

Also cleaned up minor wording and type formatting in the existing property list.

Checklist

• I fully tested it as developer / designer and created unit / integration tests
• I documented it (or no need to document or I will create a separate documentation issue)

• Fixes Angular - Update extensible table document to introduce infinite scroll and multiple selection features #23695

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