[4.3] Cherry-picks related to `ResourceLoader`

[RandomShaper]

In order to be sure everything worth cherry-picking into 4.3 is included, and also to help a bit with the correct order and conflict solving, I'm making this PR, cherry-picking the following 4.4-targeting PRs (in this exact order):

• #93336
• #94801
• #94169
• #95477
• #96108
• #96218
• ~#95508~ ~2024-09-23:~ Removed (reason: https://github.com/godotengine/godot/pull/95508#issuecomment-2360639805)
• #94920
• #96593
• #96617 🆕
• ~#96656 🆕🆕~ 2024-09-17: Removed (reason: https://github.com/godotengine/godot/pull/93605#issuecomment-2355128103).
• #96904 🆕🆕🆕
• #97370 🆕x4

[AThousandShips]

See:

• https://github.com/godotengine/godot/pull/97180

[akien-mga]

Thanks!