docs/features: Update extensions for swr

docs/features: Update extensions for swr

The following are all supported:

- GL_ARB_shader_atomic_counters
- GL_ARB_shader_image_load_store
- GL_ARB_shader_image_size
- GL_ARB_texture_multisample
- GL_KHR_texture_compression_astc_ldr
- GL_KHR_texture_compression_astc_sliced_3d
- GL_OES_texture_float
- GL_OES_texture_float_linear
- GL_OES_texture_half_float
- GL_OES_texture_half_float_linear

Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7281>