Remove dedicated "show editing toolbar" action from 3d windows

[nyalldawson]

Instead add right-click menu to main 3d window toolbar to toggle optional toolbar visibilty, just like we do for the main QGIS window.

This avoids UI bloat in 3d map windows, and removes an action which will be rarely used.

[github-actions]

🪟 Windows builds

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Debug symbols for this build are available here.
(Built from commit 0828224)

🪟 Windows Qt6 builds

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(Built from commit 0828224)

[uclaros]

😿
My points against this:

• I don't think the 3d view toolbar is bloated, it only has 12 buttons, which is 44 less than the main windows' default. If you think that's too many, I'd rather remove the semi-broken on-screen navigation relic button instead.
• Point cloud editing might be niche, but the toolbar may accommodate other layer types' editing tools in the future. Vector layer 3d editing is a much requested feature.
• Main window has the editing toolbar visible by default
• Toolbar position and visibility persist in the main window
  But more importantly:
• There is no visible clue that the toolbars are dynamic and one needs to right click. In the main window, toolbars have a handle and are movable. Users (or at least many of them) expect it to be right clickable, and even if not, there is a menu entry to manipulate the toolbars. In the secondary views however, both 2d and 3d, this is not the case.
• Right click does not work on the big blank space to the right of the last item of the main toolbar