Add support for typing of functions with variable/optional arguments in Source Typed

[zhaojj2209]

Currently, the Source Typed type error checker is unable to handle typing of the following cases:

• Pre-declared functions with variable/optional arguments (e.g. display, math_max)
• Spread syntax (e.g. functions with variable number of arguments, spreading of arrays)

The relevant code in typeErrorChecker.ts have been marked with TODOs.

Implementation should be made easier once the type inference feature is removed, as the types used by the type error checker would no longer be constrained by the type system used in the type inference feature, and can be expanded more easily to include variable/optional function types.