os: add os.{get,set}Priority()
Allow Node to set and set process priorities. This PR requires #22365 (libuv update) and #22394 (bug fix in os module). Ignore the first commit, which is just the libuv update from #22365.
Checklist
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make -j4 test
(UNIX), orvcbuild test
(Windows) passes -
tests and/or benchmarks are included -
documentation is changed or added -
commit message follows commit guidelines