Add glTF sampler filters and wrap modes enums

[matthew-rister]

Problem

cgltf_sampler defines filter and wrap modes using cgltf_int, which requires referencing the glTF specification to interpret those integers.

Solution

To fix this, enumerations representing valid glTF sampler filter and wrap modes are introduced. For backward compatibility, these enumerations retain their original integer values to allow implicit conversion to cgltf_int.

Testing

Project tests were run using tests/test_all.py on Windows (MSVC 19.41.34123) and Ubuntu (GCC 13.2) which passed without any errors.

Notes

• cgltf_filter_type includes cgltf_filter_type_undefined = 0 because the glTF specification indicates, "Client implementations SHOULD follow specified filtering modes. When the latter are undefined, client implementations MAY set their own default texture filtering settings." This will always be the default value when not specified because samplers are allocated with calloc.
• cgltf_wrap_mode omits the suffix _type because there is precedent with a similar enum: cgltf_alpha_mode.

Closes #256

[zeux]

fwiw I've tested this in gltfpack and it works correctly (no app code changes required). It would probably be more consistent with the rest of the code to omit the _default enum value for wrap mode (and just use _repeat explicitly) but it works either way.

[matthew-rister]

fwiw I've tested this in gltfpack and it works correctly (no app code changes required). It would probably be more consistent with the rest of the code to omit the _default enum value for wrap mode (and just use _repeat explicitly) but it works either way.

Thank you for confirming this change works in gltfpack without further modification. The motivation for cgltf_wrap_mode_default came from the glTF specification which explicitly indicates a default value for wrap modes so it felt appropriate to represent that as part of the API. However, I see this convention isn't used elsewhere in the library so I'm happy to remove it to maintain consistency.