mi: Shortcut miDoCopy/miCopyArea based on clipList

This is maybe one more comparison, but it catches FullyObscured windows
slightly earlier, so it's kind of a wash. The important thing is this
allows for paintable but unmapped windows, which will have non-empty
clipList.
3 jobs for pre-bsa-cleanups in 13 minutes and 22 seconds (queued for 13 minutes and 16 seconds)
Status Job ID Name Coverage
  Docker Image
passed #165520
debian-testing

00:01:03

 
  Build And Test
passed #165521
autotools-build-and-test

00:10:05

passed #165522
meson-build-and-test

00:02:12