refactor(multiple): expose APIs necessary for demos (#32262)

Exposes some APIs used in the demos instead of accessing the private `_pattern`.

(cherry picked from commit f0e411b)

Co-authored-by: Kristiyan Kostadinov <crisbeto@abv.bg>

Author: ok7sai

src/components-examples/aria/combobox/combobox-readonly/combobox-readonly-example.ts

@@ -51,18 +51,17 @@ export class ComboboxReadonlyExample {
     afterRenderEffect(() => {
       const popover = this.popover()!;
       const combobox = this.combobox()!;
-      combobox._pattern.expanded() ? this.showPopover() : popover.nativeElement.hidePopover();
+      combobox.expanded() ? this.showPopover() : popover.nativeElement.hidePopover();
 
-      // TODO(wagnermaciel): Make this easier for developers to do.
-      this.listbox()?._pattern.inputs.activeItem()?.element().scrollIntoView({block: 'nearest'});
+      this.listbox()?.scrollActiveItemIntoView();
     });
   }
 
   showPopover() {
     const popover = this.popover()!;
     const combobox = this.combobox()!;
 
-    const comboboxRect = combobox._pattern.inputs.inputEl()?.getBoundingClientRect();
+    const comboboxRect = combobox.inputElement()?.getBoundingClientRect();
     const popoverEl = popover.nativeElement;
 
     if (comboboxRect) {