Select All operator and boiler plate for future point cloud operators.
The selection code is basically copied/inspired by the curves selection
code. A lot of it could probably be moved to shared attribute selection
functions.
Note, while this patch is working well, there are some caveats
to test it:
* Shortcuts are being defined (you can see them in the Preferences). Yet
they are not working for whatever reason.
* There is no way to visualize the selection. I've been testing it by
using a Nodes tool that changes the material based on selection.
Pull Request: https://projects.blender.org/blender/blender/pulls/134450
1e87818808