Harmonize 3D map view widget with 2D ones to display the map theme drop-down menu

[ismailsunni]

Description

• fixes Harmonize 3D map view widget with 2D ones to display the map theme drop-down menu #33954
• Add map theme switcher for 3D view in the toolbar, like the 2D view one (will be disabled if the terrain is a mesh)
• Remove map theme combo box from the 3D config dialog
• Preview
  
• Set map theme logic is taken from the original 3D map view config
• Map theme switcher logic is taken from the 2D one.

[nirvn]

@ismailsunni , I like this a lot, you get my seal of approval UI/UX-wise.

[ismailsunni]

Thanks @nirvn , credit to @DelazJ who gave the idea, I merely put the code :)

[wonder-sk]

This all looks great!

With mesh-based terrain, that's a limitation of the mesh terrain generator - hopefully in a future version it will be able to show arbitrary map theme!

[nyalldawson]

@ismailsunni can you fix the conflict here?

[ismailsunni]

@nyalldawson done, waiting for the checks now

[ismailsunni]

Please don't merge this PR. After I rebase the code to fix the conflict, it will crash QGIS whenever I open the 3D view. It was fine though before rebasing the code.
I will try to check this first.

[ismailsunni]

I fixed the crash issue, and it should be ready to merge if the test pass.