Menu: make trigger button float when button with isFloating is slotted

[RasmusKjeldgaard]

Which issue does this PR close?

This PR closes # (insert issue number here)

What is the new behavior?

This is a proposal for a migration path for FAB-sheet-like behavior in Kirby now that Action Sheet (and therefore FAB-sheet) is deprecated in v9 and removed in v10.

With this addition kirby-menu will recognize whenever a button with isFloating set to true is slotted as a custom button, and position itself in the bottom right side of its containing element.

This could be extended with css props to enable custom placement.

Does this PR introduce a breaking change?

• Yes
• No

Are there any additional context?

Checklist:

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When the pull request has been approved it will be merged to develop by Team Kirby.