Do not re-check visibility or re-render shadow maps for point and spot lights for each view

[coreh]

Objective

If I understand it correctly, we were checking mesh visibility, as well as re-rendering point and spot light shadow maps for each view. This makes it so that M views and N lights produce M x N complexity. This PR aims to fix that, as well as introduce a stress test for this specific scenario.

Solution

• Keep track of what lights have already had mesh visibility calculated and do not calculate it again;
• Reuse shadow depth textures and attachments across all views, and only render shadow maps for the first time a light is encountered on a view;
• Directional lights remain unaltered, since their shadow map cascades are view-dependent;
• Add a new many_cameras_lights stress test example to verify the solution

Showcase

110% speed up on the stress test 83% reduction of memory usage in stress test

Before (5.35 FPS on stress test)

After (11.34 FPS on stress test)

Testing

• Did you test these changes? If so, how?
  • On my game project where I have two cameras, and many shadow casting lights I managed to get pretty much double the FPS.
  • Also included a stress test, see the comparison above
• Are there any parts that need more testing?
  • Yes, I would like help verifying that this fix is indeed correct, and that we were really re-rendering the shadow maps by mistake and it's indeed okay to not do that
• How can other people (reviewers) test your changes? Is there anything specific they need to know?
  • Run the many_cameras_lights example
  • On the main branch, cherry pick the commit with the example (git cherry-pick --no-commit 1ed4ace01) and run it
• If relevant, what platforms did you test these changes on, and are there any important ones you can't test?
  • macOS

[alice-i-cecile]

@coreh, are you able to resolve the merge conflicts here? :)

[BenjaminBrienen]

I'll take a look at this tomorrow and see if the merge conflicts are simple enough.

[alice-i-cecile]

I can't merge this: CI is failing due to disallowed platform-inconsistent float methods. It's an easy fix at least :)