Optimize parallax VRAM usage (#37180)

Optimize parallax VRAM usage (#37180)

* Disable parallax texture preloading

Many parallax layers are specific to a single map and will likely never be loaded for the duration of the game. Save VRAM by not loading them always.

Requires engine master

* Put generated parallax identifier in texture name

Makes it show up properly in debugging tools

* Don't load generated parallaxes multiple times

Many parallax prototypes re-use the same generated parallax configs. These generated parallaxes were being loaded multiple times at once, which was a massive waste of VRAM.

We now move these into a separate cache for deduplication. I had to write a lot of logic to handle loading cancellation and ref counting. Yay.

Also fixes some spaghetti with the previous parallax loading system: cancellation didn't work properly, give proper names to generated texture names, etc.

This saves like 100+ MB of VRAM.