Cleanup typer part 3: Preparing to merge type_value and type_expression (!1109) · Merge requests · ligolang / LIGO · GitLab

This MR prepares the work for #1182 (closed)

There seem to be two main differences:

records and variants (single case "Row" vs. T_Record and T_Variant)
constants (constant itself + argument in one case, T_App(t, t) in the other)
constants are treated like keywords (they are not properly scoped) and are not using an OCaml variant, instead they are just type variables which happen to have the right name: https://gitlab.com/ligolang/ligo/-/blob/310c22d2/src/passes/09.5-inference/wrap.ml#L11-55