Test #1476 in th/T1476
Test that nested pattern splices don't scope (#1476).

Test case: th/T1476b.
Fix #1476 by making splice patterns work.

Unfortunately, splice patterns in brackets still do not work
because we don't run splices in brackets. Without running a pattern
splice, we can't know what variables it binds, so we're stuck.

This is still a substantial improvement, and it may be the best
we can do. Still must document new behavior.
Release notes for #1476, #7484.
Remove unboxed Int# fields from NameFlavour (#9527)
Derive Generic for TH types (#9527)
Untabify template-haskell.
Remove unused import from TH/PprLib