mesa: update features.txt to reflect EXT_dsa status

mesa: update features.txt to reflect EXT_dsa status

All features from the EXT_dsa spec are implemented.

Interactions with other specs:
- GL_AMD_gpu_shader_int64: not needed, since it's not enabled in
  compatibility profile.
- GL_ARB_bindless_texture is DONE
    "INVALID_OPERATION is generated when calling various functions
    to modify the state of a texture object from which handles have
    been extracted"
- GL_ARB_buffer_storage/GL_EXT_buffer_storage is DONE (NamedBufferStorageEXT function)
- GL_ARB_texture_storage is DONE (3 TextureStorage*DEXT functions)
- GL_ARB_vertex_attrib_binding is DONE (6 VertexArray* functions)
- GL_EXT_external_buffer is not supported by Mesa

Reviewed-by: Marek Olšák <marek.olsak@amd.com>