Refactor LetBlock, allow single LetIn

Switch to registry pattern for TypeChecker.for

Refactor TextLiteral typecheck

Refactor If typecheck

Refactor OperatorListConcatenate typecheck

Start refactor of list concat

Refactor OperatorRecursiveRecordMerge typechecker

Refactor OperatorRightBiasedRecordMerge typechecker

Refactor OperatorRecursiveRecordTypeMerge typecheck

Refactor List typecheck

Refactor Optional/None typecheck

Refactor AnonymousType typecheck

Refactor Record typecheck

Refactor RecordSelection typecheck

Refactor RecordProjection typecheck

Refactor Union typecheck

Finish merge refactor

Refactor Function annotate

Refactor Forall typecheck

Refactor some of typecheck

Get closer to fitting the metrics