New Type Checker: Check Functions Pass

[Vengarioth]

Old code: https://github.com/Vengarioth/xshade/blob/master/src/type_system/type_check.rs#L94-L124

• Create a pass in passes/ast/type_checking
• Add function type to symbol table
• Add function as symbol to the symbol table
• Type check arguments
• Type check return type (not if it actually returns the correct type)
• Set call signature for function type
• Test the pass