Ryan Scott authored Feb 15, 2021 and Marge Bot committed Feb 16, 2021

This adds a new `otycon` production to the parser that allows for type
constructor names that are either alphanumeric (`tycon`) or symbolic
(`tyconsym`), where the latter must be parenthesized appropriately.
`otycon` is much like the existing `oqtycon` production, except that it does
not permit qualified names. The parser now uses `otycon` to parse type
constructor names in `ANN type` declarations, which fixes #19374.

To make sure that all of this works, I added three test cases:

* `should_compile/T19374a`: the original test case from #19374
* `should_fail/T19374b`: a test that makes sure that an `ANN` with a qualified
  name fails to parse
* `should_fail/T19374c`: a test that makes sure that an `ANN type` with a
  qualified name fails to parse