Update pipeline desc when sample count changes * If the sample count changes when calling glFramebufferTexture2DMultisampleEXT, we need to update pipeline desc to ensure it is the same as the API requires. * Add a new end2end test to verify. Bug: angleproject:422611722 Change-Id: I7de7d3d17513cf03f5e24baa2db83633a229b4b8 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/6623419 Reviewed-by: Shahbaz Youssefi <syoussefi@chromium.org> Reviewed-by: Yuxin Hu <yuxinhu@google.com> Auto-Submit: Aurora Zhang <Aurora.Zhang@arm.com> Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>