Rework mod content installation.

[pchote]

This PR removes the magic cross-mod inheritance that was originally implemented to support the long-defunct oramod archive format.

The key benefits here are:

• Removal of implicit and magic behaviours around mod.yaml, filesystems, and translations
• Clean separation between installation and runtime (mods that ship all their own assets can now completely ignore the installation logic 🎉)
• Another step towards upstreaming TDHD by allowing first-class support for mod-specific installation behaviours

[pchote]

Fixed and rebased.

[PunkPun]

• D2K detection of assets is wrong! While the quick install itself doesn't fail, the game fails to load and puts you back into the d2k-content mod. Note that with the installed files you are able to play on bleed, just not on this branch
• after I install everything from remastered it is no longer detected
• after installing required files from the remaster, I still have the option to quick install (no warning)

[pchote]

Rebased, fixed, and tested quick install + at least one advanced install method for all mods.

D2K detection of assets is wrong!

Oops, thats what I get for rushing things without proper testing.

after I install everything from remastered it is no longer detected

If you mean for RA, then this is expected because the remaster doesn't include the soviet briefings and therefore isn't a valid source for that content package.

after installing required files from the remaster, I still have the option to quick install (no warning)

This actually has always been the case, so i'd prefer to leave any changes to this to a different PR!

[PunkPun]

LGTM, we'll want more thorough playtesting when playtest launch

[PunkPun]

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