renderer/native: Add tracing for 2nd GPU copies

These traces allow seeing how long the copy operations stall in libmutter, and
which copy operations actually get used.

GNOME/mutter!615
4 jobs for !615 with mr/primary-copy in 6 minutes and 40 seconds
detached
Status Job ID Name Coverage
  Review
passed #328462
check-commit-log

00:00:24

 
  Build
passed #328463
build-mutter

00:02:40

 
  Test
passed #328465
can-build-gnome-shell

00:01:34

passed #328464
test-mutter

00:03:35