Enable -Wexit-time-destructors for all in-tree library targets and
update process-lifetime library statics so they no longer register
exit-time destructors. Long-lived caches, lookup tables, singleton
registries, and generated constants now use NeverDestroyed or leaked
references where the data is intended to live until process exit.
Update LibWeb, LibLine, and the binding generators so regenerated
sources follow the same rule instead of reintroducing destructed
statics.
Let's not have LibRegex be the home of LibUnicode FFI. Move these to
LibUnicode so that we can:
1. Use these helpers in other libraries more easily.
2. Swap out icu4c methods with icu4x methods all within LibUnicode.
