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 master in 9 minutes and 18 seconds (queued for 2 minutes and 7 seconds)
Status Name Job ID Coverage
  Docker Image
passed debian-testing #165537

00:00:29

 
  Build And Test
passed autotools-build-and-test #165538

00:06:57

passed meson-build-and-test #165539

00:01:51