Defer the attachment of GL stencil buffers

This will allow us to use a single FBO for
EXT_multisampled_render_to_texture, that we modify on-demand depending
on whether we need MSAA.

Bug: chromium:1222095
Change-Id: Ife2d743e28833521d785e4bf0e20de593c492a9a
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/442736
Commit-Queue: Jim Van Verth <jvanverth@google.com>
Reviewed-by: Brian Salomon <bsalomon@google.com>
5 files changed