[WIP] Typecheck procedure signatures + Various changes

[Pieter12345]

Changes

• Typecheck procedure signatures. This assumes that procedure signatures cannot be redefined after the initial declaration, which does not hold for the current implementation. Enforcing this should be done at a later point as this potentially breaks user scripts.
• Disallow mandatory-after-optional params in proc signature typechecking.
• Prevent injected @arguments variable overwriting an explicitly declared procedure parameter named @arguments.
• Initialize procedure varargs parameter with an empty array if it matches no arguments. Prevents varargs parameter value being CNull.UNDEFINED when it has no matching arguments.
• Add compile error on missing returns in procedures.
• Implement function signatures and getReturnType() in control flow manipulating functions.
• Throw exception when invoking proc forward declaration (opposed to not doing anything and returning void, regardless of the declared proc return type).
• Add none type and missing return false error tests. These ensure that mentioned typechecking and missing return error changes do not break the obvious use-cases that can be expected to be affected.

WIP

This PR is marked as work-in-progress for the following reasons that should be addressed before merging:

• dor() and dand() typechecking implementation needs to be implemented in order to prevent missing return errors for returns within them that are guaranteed to run.
• This PR should be tested against large code bases to identify potentially undesired breaking changes.