swr: fix support for GL_ARB_copy_image extension

This commit fix support and adjusts the capabilities
returned by the SWR driver and the documentation
to correctly report the GL_ARB_copy_image extension.

Reviewed-by: Alok Hota <alok.hota@intel.com>
10 jobs for !981 with swr_GL_ARB_copy_image in 9 minutes and 35 seconds (queued for 1 second)
detached
Status Job ID Name Coverage
  Containers Build
passed debian #339718

00:00:23

 
  Build+Test
passed meson-clang #339720

00:08:34

passed meson-clover #339724

00:08:56

passed meson-main #339723

00:07:06

passed meson-swr-glvnd #339719

00:07:18

passed meson-vulkan #339725

00:02:30

passed scons-llvm #339727

00:03:48

passed scons-nollvm #339726

00:04:36

passed scons-swr #339721

00:09:08

passed scons-win64 #339722

00:05:01