feat(gui): add some esoteric VTF formats to the texture preview #700

Job	Run time
build-linux (Debug, gcc, VPKEdit)	8m 29s
build-windows (Debug, msvc, VPKEdit)	2m 7s
build-windows (Debug, msvc, StrataSource)	2m 15s
build-linux (Debug, gcc, StrataSource)	8m 42s
build-windows (Release, msvc, VPKEdit)	2m 14s
build-linux (Release, gcc, VPKEdit)	8m 27s
build-windows (Release, msvc, StrataSource)	2m 14s
build-linux (Release, gcc, StrataSource)	8m 43s
deploy	0s
	43m 11s

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