* Use hash of ADT name and constructor idx to generate tag, add reverse mapping to module and use where appropriate

* Lint and build fixes

* Add round-tripping test for getting constructors by tag

* Use int64_t everywhere for tags

* Add additional identity check

* Bring out _arg_to_ast again

* Use 8-bit hash of GTV name as MSB of tag, index as LSB for more readable tags

* Use int32 instead of int64 for tag