Menu button updates for table

[mollykreis]

Pull Request

🤨 Rationale

Some changes need to be made to the menu button before it can be used within the table for the action menu. Specifically, those changes are:

• adding a beforetoggle event
• having the menu button find the slotted menu when it is nested within multiple slots

See #956 for more details.

👩‍💻 Implementation

• Add beforetoggle event to the menu button that is fired before the menu opens or closes
• Add Angular & Blazor support for the beforetoggle event
• Change the logic for finding the slotted menu. We can no longer use a filter in the template to find slotted elements with a role of menu because this won't match slot elements. Instead, the template assigns all slotted elements to the slottedMenus array, and the getter for menu finds the menu, which may be nested within slot elements.

🧪 Testing

• Manually tested that the beforetoggle event handler works correctly in Blazor & Angular
• Added auto tests for the beforetoggle event works correctly for the web components
• Basic manual testing in Storybook that the component still behaves as expected
• Added tests that the focus & menu opening behavior works correctly when the menu is nested in an additional slot

✅ Checklist

• I have updated the project documentation to reflect my changes or determined no changes are needed.