meta: Avoid _swrast_BlitFramebuffer in the meta CopyTexSubImage code.

meta: Avoid _swrast_BlitFramebuffer in the meta CopyTexSubImage code.

This is a replacement for bd44ac8b5ca08016bb064b37edaec95eccfdbcd5
that should actually work.

Fixes Piglit's copyteximage-border on swrast, as well as one of
es3conform's packed_pixels_pixelstore test.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=78546
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=77705
Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Chris Forbes <chrisf@ijw.co.nz>
Cc: "10.2" <mesa-stable@lists.freedesktop.org>