Add class constraints for built-in classes

[sezna]

This PR exposes some relevant built-in classes via class constraints.

Changes

• Add TypeParameter, ClassConstraint, and ConstraintParameter AST nodes to represent the notion of a generic type that might have class constraints, and constraints that may have parameters (e.g. Exp[Int]).
  • update visitors accordingly
• Ty can now contain arbitrary constraints
• Add notion of primitive classes to the AST
• Update constraint checking algorithm to check type parameters for primitive constraints at callable decl time
• Update constraint generation algorithm to add additional user-specified constraints to arguments that are passed in to callables (fn constrained_ty)
• Add completions for primitive classes to the language service
• Adds a sample describing class constraints

tiny changes:

• Add docstrings discretionally
• Remove some unnecessary derives
• Tried to clarify and unify jargon around classes, constraints, parameters, and arguments in general
• Some expect_tests were updated in minor ways as their underlying types changed (Ty and TyParam, for example)
• Improve an error message for MissingTy (it mentioned something about global types not being inferred when 99% of the time it does not apply to a global type, it applies to a callable parameter with a missing type)

TODO for this PR

• Track down why duplicate constraints are getting generated
  I did not want to block reviewing this PR on this bug, since it isn't an experience breaker, but I would like to get it resolved before this goes in. Sometimes, multiple errors are rendered, and I've narrowed it down to duplicate constraints getting generated. I could store constraints in some sort of Set, so they're deduplicated, but I'd rather figure out what we are repeatedly visiting to generate those constraints instead of deduplicating afterwards. I'll be tracking this down while the PR is reviewed.

[github-actions]

Change in memory usage detected by benchmark.

Memory Report for f387f6f

Test	This Branch	On Main	Difference
compile core + standard lib	19517141 bytes	17964197 bytes	1552944 bytes

[github-actions]

Change in memory usage detected by benchmark.

Memory Report for 81431fb

Test	This Branch	On Main	Difference
compile core + standard lib	19517141 bytes	17964197 bytes	1552944 bytes

[github-actions]

Change in memory usage detected by benchmark.

Memory Report for 756cbab

Test	This Branch	On Main	Difference
compile core + standard lib	19517141 bytes	17964197 bytes	1552944 bytes

[sezna]

I opened #2007 to replace this, since there are too many commits and it is hiding comments.