docs/features: Add GL_EXT_multisampled_render_to_texture

Currently only a6xx, panfrost added later in series.

Signed-off-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Acked-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/6161>
1 file changed