Emitter: Replace old emit_assign with emit_rebox_to_any (mostly internal).
Emitter: Replace old emit_assign with emit_rebox_to_any (mostly internal).

The latter function wraps around emit_rebox_value, which ensures that bare
variants are never directly put into an any without being put into an enum
class value first.

There's probably a bug or two fixed by this. If nothing else, consistency!

boardwalk/lily,crasm/lily,crasm/lily,boardwalk/lily,crasm/lily