Valve BSP, WAD, and external texture support

[Toodles2You]

Valve format support and external WAD texture support!

I originally implemented these changes for vkQuake. @vsonnier suggested porting them here to benefit the broader modding community.

Quick overview:

• Textures are loaded from WADs if they aren't embedded within the map itself
• WAD3 full color textures
• BSP30 24-bit RGB lighting

See Novum/vkQuake#753 for more details. This PR contains all of the changes & fixes discussed there.

Test maps

[sezero]

• unnecessary whitespace changes in wad.h
• unnecessarily (wrongly) dropped void from W_LoadWadFile()
  (C23 would reject that, for e.g.)
• source_name must be const char* in Mod_LoadTextures()
  (C23 would reject that, for e.g.)
• Mod_LoadWadFiles() must accept a qmodel_t* parameter
• build failed without BSP29_VALVE defined
• a few whitespace inconsistencies here and there

The attached patch (against yours) addresses those above, and makes
the diff a bit cleaner.

P.S.: TYP_MIPTEX_PALETTE clashes with TYP_SOUND, but I guess that's
unavoidable.

Please amend the changes and then let's see if others have anything
to say. E.g.:

cd quakespasm && patch -p1 < patch.txt
git commit -a --amend
git push --force

CC: @ericwa, @andrei-drexler, @Shpoike

patch.txt

[Toodles2You]

I reverted the changes to gfx.wad handling. You pointing out the dropped void from W_LoadWadFile made me realize they were unneeded remnants of an earlier iteration of the WAD loading.

[Toodles2You]

Improved the safety checks for WAD3 texture loading.

Also, BSP embedded WAD3 textures are reloaded in memory. QS doesn't load all of the mip levels, so reloading textures (gl_fullbrights for example) caused them to load data from the wrong offset.

[sezero]

@ericwa, @andrei-drexler, @Shpoike: Last call for a review for this before this weekend.

P.S.: There is a warning from my old compiler:

wad.c: In function 'W_AddWadFile':
wad.c:191:2: warning: dereferencing type-punned pointer will break strict-aliasing rules

It for that evil tyype-punning *(int *)&header.identification[0]
Maybe I'll do something for that later..

[sezero]

OK, this is in now. Please create new tickets if any issues are found with it.

Thanks.

[Toodles2You]

Awesome! I'll keep an eye out.

Thank you for your time, and for the code review.