feat(MenuTrigger): Extend selector to match documentation

[michaelkrog]

Feature Description

The description of MenuTrigger says:

The ngMenuTrigger directive is used to open and close menus. It can be applied to any interactive element (e.g., a button)...

But in the reality the selector is bound to the button element making it cumbersome to use with custom button components.

@Directive({
  selector: 'button[ngMenuTrigger]',
  exportAs: 'ngMenuTrigger',
  ....
})

https://github.com/angular/components/blob/main/src/aria/menu/menu-trigger.ts#L44

Use Case

In our case we have a need to trigger the menu using different elements in our design system fx. our custom button component. The current selector requires us to have a button around our button fx:

<button ngMenuTrigger>
  <lm-button/>
</button>

It causes a focus trap as our custom button is always focusable and ngMenuTrigger forces the wrapping button to also be focusable.