Enable anisotropic filtering for replacement textures with mipmaps

[hrydgard]

This should fix the issue seen in #17891 where if the game itself doesn't use mipmaps, but the replacement texture does, anisotropic filtering wasn't enabled.

Although I think we could be more generous about enabling anisotropic filtering - possibly we should just always turn it on, if enabled, instead of only using it together with mipmapping. It does help with the look of filtering textures at steep angles even if they don't have mipmaps by reducing shimmer. That change though I'll do after the release.

[unknownbrackets]

I thought we used to always use it when enabled, as long as it wasn't nearest. I guess that changed?

-[Unknown]

[hrydgard]

I think we didn't want to apply it in slope/fixed level modes, to be safe from games doing weird tricks with miplevels. But might be too conservative and led to more complicated logic which led to this, I guess.

Not 100% sure this is the right sequence of events though.