Add VoxelGI bake canceling and progress UI improvement

[badsectoracula]

This enables the "Cancel" button in the VoxelGI baking progress window similar to #99483 and improves the progress UI so that it shows the current progress in a more granular fashion (i.e. it takes into account the combined work the meshes to plot and adds SDF building progress).

Like with the lightmap build, i mainly tested it with the global illumination demo, though i had to increase the subdivision to 512. In devbuilds the process is much slower and easier to test for leaks, etc. In production build the slowest part is SDF building (which is also the part that previously had no progress report).

This does slow down the baking progress a bit but the difference is an increase of about 1.13% on my PC. With 5 runs with and without the PR in a production build the baking time increased from an average of 15319 millseconds (~15.3 seconds) to 15493 milliseconds (~15.5 seconds), which i think is acceptable as with small voxel boxes it wouldn't make a noticeable difference but with larger voxel boxes you'd want some way to monitor the progress and cancel the bake.

[Calinou]

Tested locally, it works as expected.

I didn't notice any memory leaks when canceling the bake at various points in time.

[Repiteo]

Thanks!