Fix GL_TEXTURE_MAX_ANISOTROPY_EXT not being optional

Merge branch 'master' into tmp-texture-sampler

Cleanup: GPU: Remove uneeded texture bind for texture sampling parameters

GPU: Texture: Avoid using anisotropic filtering on all textures.

This limits anisotropic filtering to image textures (comming from
GPU_texture_from_bindcode).

GPU: Texture: Replace internal sampler state by explicit state object

This is closer to vulkan design and allow for easier state management in
the future. For instance, adding the ability to bind the texture twice
with different sampler params.

GPU: Draw: Move filter parameters to sampler_state.

GPU: Texture: Enable support for multiple texture units bind.

This makes possible to bind a texture up to GPU_TEX_MAX_BIND texture units.
Multiple binds can be useful to sample a texture using different sampler
state.