Improve texture replacement cache and allow read from zip

[unknownbrackets]

This makes a few changes:

1. Moves decoded image data caching to cache by filename, rather than by cache key. This reduces duplicate cache data in memory.
2. Imposes pressure on the cache after 1 GB maximizing at 4 GB, linearly increasing decimation aggressiveness.
3. Allows the use of a textures.zip file inside PSP/TEXTURES/GAME12345/ in place of textures.ini, for better performance.

Note: I'm pretty sure that pointers to values in std::unordered_map are permanent until erased, but correct me if I'm mistaken.

To use textures.zip:

• textures.ini must be at the root of the zip, not inside a subfolder. Don't zip the folder, add the contents themselves.
• It's recommended to use "store" compression mode (zim or zip files will already be compressed, so zip compression will just waste performance.)
• Save new textures works, but won't save into the zip file and the saved files won't be used.
• Make sure textures.zip is inside the game-specific folder, exactly where textures.ini would've gone.

Currently there's no way to directly install a textures.zip file, and as noted it's a bit more restrictive than the installer allows (i.e. with textures.ini required at the root.) That said, the installer could be changed to just copy the zip into place.

Fixes #16135.

-[Unknown]

[hrydgard]

Iterators in unordered_map get invalidated when the map rehashes, which it can do when it grows. See https://stackoverflow.com/questions/16781886/can-we-store-unordered-maptiterator for example.

Will actually look at the code now - or actually later.

[unknownbrackets]

I think references are fine, though: https://stackoverflow.com/questions/39868640/stdunordered-map-pointers-reference-invalidation / https://news.ycombinator.com/item?id=27597471. I'm mostly unsure because I honestly have no idea what the node type stuff is, i.e. this question: https://stackoverflow.com/questions/72255609/stdunordered-map-insert-invalidates-only-iterators-but-not-references-and-poin.

-[Unknown]

[hrydgard]

Yeah you're right, those should be fine, unlike iterators - if it was allowed to move the nodes in memory, a lot of stuff would break.

[rorowong888]

Thank you so much for this act. Which is a hugh upgrade for reading texture pack via zip packing method.
Some of the hd pack especially racing game is very largely if using old version.But now ,that is no longer after 1.14.4.
Thank again hrydgard and keep it up 👍