Add support for context menu for viewport tab title and selected container's children list

[abey79]

What

As the title says ☝🏻
Fixes #5300

To meaningfully accomodate with these additional contexts, the context_menu_ui_for_item function now support various modes of interaction with the selection:

• blueprint tree: consider the multi-selection if the clicked item is part of it, otherwise set selection to clicked item
• tab title: always set selection to clicked item
• container selection panel children list: ignore the selection

Checklist

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[Wumpf]

interesting idea with SelectionUpdateBehavior. Personally, I find the choices a bit arbitrary, but works out overall to ux that I would not call intuitive :)

[abey79]

interesting idea with SelectionUpdateBehavior. Personally, I find the choices a bit arbitrary, but works out overall to ux that I would not call intuitive :)

I agree, it's totally ad hoc, and based on what made more sense to me for the various contexts involved.