Add support for parsing polymorphic type declarations

[shonfeder]

Closes #1296

Adds support for two new kinds in the types IR:

1. Type abstraction, giving us type-level functions
2. Type application, giving us type-level function application

Closes #1297

Adds support for parsing polymorphic type declarations and type constructor application. This enables forming types of the kinds above as follows:

1. Type abstractions is produced only by type declarations of the following form:

   type T[a,b] = (a, b)

   Similar to operator declarations, there are parsed into the assignment of a name to an abstraction. I.e., in this case, T = Λ(a, b).(a,b)

2. Type application generalizes our current special-cased support for List and Set. E.g., we apply the polymorphic T defined above as T[int, str].

[shonfeder]

As is always the case with changes to the parser, nearly all the lines in the diff are from updates to fixtures and the generated parser code.

[bugarela]

I can't wait to start using this!
Just left a few comments, specially on the ToIRListener where we should have fallbacks to enable error recovery on this stage of parsing.