MenuButton changes and additions

[vnbaaij]

This PR fixes #1593 and #1594 by:

• adding a FluentOverlay so clicking outside the menu closes it
• Adding a ButtonAppearance parameter to make changing the button appearance possible

An example has been added to the deom to show this.
Example of the ovverlay:

Also, source comments have been added and a documentation section is added to the menu button page.

[Rocky-25]

This looks good, just wondering if the icon colour should be Accent if it's not an accent button?
FluentMenuButton.razor.cs line 66
_iconColor = ButtonAppearance == Appearance.Accent ? Color.Fill : Color.FillInverse;
should be:
_iconColor = ButtonAppearance == Appearance.Accent ? Color.Fill : Color.Accent;

Icons in a button seem to use this colour?

[vnbaaij]

No, in this case it is not really used as an icon but more as a text element (which happens to be rendered with an icon) so same color as text

[Rocky-25]

Okay that's fair enough. Thanks for making the changes Vincent.