Rename TermConstructor to CurriedTermConstructor.
Rename TermConstructor to CurriedTermConstructor.

This rename prepares for introducing UncurriedTermConstructor which
will allow to clarify the role of lift-η-const-rec.

Old-commit-hash: b9de3c413f5a2a2015d3114bfb8483ab3078cc06

inc-lc/ilc-agda