Add sprite loaders for C&C Remastered Collection

[pchote]

This PR adds sprite loaders for object (unit/structure/vfx/etc) and terrain artwork.

Object artwork is packaged as a zip file containing tga images and json metadata.
Terrain artwork is loose dds files that will need additional tileset support before a mod can use them. As noted in the code, this is intended as a first implementation of DDS that I expect we will eventually rewrite to keep the texture data compressed all the way through to the GPU.

This is best tested by combining with #18443 and then modifying TD's mod.yaml to add /path/to/TEXTURES_TD_SRGB.MEG in the Packages list; ShpRemastered, Dds to the SpriteFormats list and .ZIP, .DDS to the AssetBrowser SupportedExtensions list. The sprites can then be viewed in the asset browser.

[pchote]

Note to self: look into https://www.nuget.org/packages/pfim as an option to offload my (too?) minimal tga and dds parsing.

[pchote]

Note to self: SRGB != RGB. Before we start actually using these ingame, SpriteFrameType and SheetBuilder should gain a way to track SRGB data so that the texture can be uploaded with internalformat GL_SRGB8_ALPHA8.

[pchote]

There are a few misc unpackaged TGA images that we need to load, so I will need to refactor out a separate TgaLoader.

[pchote]

Updated:

• Rewritten using Pfim for file parsing
• Added TgaLoader
• Moved TgaLoader DdsLoader to Mods.Common
• Changed ShpRemasteredLoader to reuse the new TGA code instead of duplicating it

This should now be significantly easier to understand and review.

[abcdefg30]

Isn't putting those in Mods.Common running contrary to #12775?

[MustaphaTR]

Isn't putting those in Mods.Common running contrary to #12775?

Neither .tga or .dds are Westwood formats.

[pchote]

Indeed, both are widely used formats in games so I felt it more appropriate to put these in Common, and the remaster-specific wrapper in Mods.Cnc.

[abcdefg30]

Neither .tga or .dds are Westwood formats.

The larger idea was to move specific formats out of common, but if they are more widely used it's ok I guess.

[pchote]

Rebased.

[pchote]

Updated to use the plumbing from #18938.

[pchote]

Rebased.

[reaperrr]

The larger idea was to move specific formats out of common, but if they are more widely used it's ok I guess.

The idea on my end was mostly about moving support of proprietary formats out of Mods.Common, so any future commercial projects using OpenRA's engine don't have to rip anything out of Common for legal safety and just need to drop the Westwood/EA-specific dlls.
I know we made an exception for ShpTS so far, since it uses non-proprietary RLZero compression and we didn't have any good alternatives at that point. Once this PR is in, it might be time now to move that as well (in its own PR).

[reaperrr]

Code looks good as far as I'm able to judge it, but not tested yet.
Needs a rebase, though.

[pchote]

Rebased.

[reaperrr]

https://github.com/OpenRA/OpenRA/wiki/Changelog-(bleed)/_compare/4bca5ac6695e3a4dac64a49437bea77c79230123...c3871d64bc2c14f20e5f707119fc6a309f3829e0