Multiple priority scheduler (#44701)

Improves the scheduler by allowing tasks to have a set priority which
will significantly improve responsiveness.

Release notes:

- N/A

---------

Co-authored-by: Yara <git@yara.blue>
Co-authored-by: dvdsk <noreply@davidsk.dev>

Cargo.lock

@@ -7239,6 +7239,7 @@ dependencies = [
  "libc",
  "log",
  "lyon",
+ "mach2 0.5.0",
  "media",
  "metal",
  "naga",