[3D] Point cloud editing paintbrush tool

[Withalion]

Description

This PR adds new tool for editing point clouds. The new tool supports free movement, size change, highlighting of already selected area. Users can change the size of selection area by scrolling and the tool starts selecting on left click + drag. Cursor also shows loading while the point cloud is edited.

Screencast_20250131_193039.mp4

Funded by: Klimadatastyrelsen

[Withalion]

This PR builds on work done in #60378

[github-actions]

🪟 Windows builds

Download Windows builds of this PR for testing.
Debug symbols for this build are available here.
(Built from commit de4cda5)

🪟 Windows Qt6 builds

Download Windows Qt6 builds of this PR for testing.
(Built from commit de4cda5)

[saberraz]

I have tried this tool. Very nice addition. Some usability issues:

• Changing paintbrush size is controlled by the middle mouse key (wheel), by rolling back and forth. This is always dedicated for map zooming in/out and it is confusing. It is best if you combine it with a hot-key.
• More the above point, it would be good to have a dedicated pixel size for the radius of the paintbrush.
• While using the tool, I pressed the Escape key and it crashed QGIS.

[Withalion]

Paintbrush tool now supports cancellation of selection while still dragging by pressing ESC and the size of paintbrush changes by CTRL + mouse wheel.