Accept GL_TEXTURE_MAX_ANISOTROPY_EXT for samplers.

Accept GL_TEXTURE_MAX_ANISOTROPY_EXT for samplers.

This usage is not explicitly specified in EXT_texture_filter_anisotropic,
but in practice all notable ES 3.0 implementations treat maximum anisotropy
as sampler state. Furthermore, it's already accepted as a valid sampler
parameter by ValidateSamplerObjectParameter in Context.cpp.

This avoids a crash when calling
glSamplerParameteri(sampler, GL_TEXTURE_MAX_ANISOTROPY_EXT, 1.f);

Bug: b/79951966
Change-Id: I4013f621781fc74a0fbfbf14ab326871fbb87b7c
Reviewed-on: https://swiftshader-review.googlesource.com/18908
Reviewed-by: Alexis Hétu <sugoi@google.com>
Tested-by: Krzysztof Kosiński <krzysio@google.com>