Make pseq robust by using seq#

Fixes #23699, fixes #23233, and adds a test for the latter.

The implementation of par was near-by to and very similar to that of pseq, and has been adjusted in an analogous way, which also allows the deprecation of par# to resume, resolving #24825.

The documentation around Control.Exception.evaluate and Note [seq# magic] has been expanded and improved, fixing #22935. The documentation around GHC.Magic.lazy and Note [lazyId magic] which was relevant to the old implementations of pseq and par has also been improved, fixing #25210.