Cherry-picks for the 4.2 branch (future 4.2.2) - 5th batch

[akien-mga]

Final_final_v3-final.psd batch for 4.2.2, to fix the critical regression in #89674.

@clayjohn evaluated what's missing from the #87392 cherry-pick, and it turns out we had missed a bunch of follow-up PRs which are also needed to really make headless shader exports reliable, and fix regressions.

The options are to:

• Cherry-pick all the remaining bits (what I've chosen to do here, on Clay's suggestion)
• Revert the Add DummyShader handling to Dummy RenderingServer to ensure shader parameters are saved in headless export #87392 cherry-pick and keep headless shader exports broken in 4.2.2, to re-evaluate in 4.2.3
• Only cherry-pick the default value init from Change shader compiler default setting to avoid doctool error #88996 which is enough to fix Crash when exporting in headless mode on Linux with Godot 4.2.2.rc2 #89674, but then there are still a number of issues that wouldn't be resolved in 4.2.2

So I took the YOLO approach, and while at it, I included the much awaited #90431 which should also be pretty safe, and directly related to these changes. This should make exporting projects on CI much more reliable from 4.2.2 onwards.

Fixes #89674.

[tokengamedev]

There was one issue I encountered -
In compatibility mode android x86 and x86_64 simulators were not launching the app. This is of low priority as X86 and x64 devices are almost nonexistent today apart from simulators. I will raise the issue if I find time to test after this merge.