GDScript: Enforce Signal Static Typing in emit & emit_signal

[SeremTitus]

Works under the following assumptions:

1. The number of arguments passed to emit or emit_signal must not exceed the number of parameters defined in the signal.
2. The types of arguments passed must match the types of the corresponding signal parameters. (excluding passing Variant)

Encourages more consistent code.

[dalexeev]

Thank you for your efforts, but please note that this only affects the static analyzer and does not provide runtime guarantees for untyped code. In the current implementation, Godot/GDScript provide runtime guarantees for all types except enumerations. (Plus, type hints for signal parameters are declarative.)

Adding appropriate checks to the core methods connect(), emit_signal(), and so on will incur some runtime penalty. Optimization will require multiple versions of these methods: a safe but slow one (for the general untyped case) and a fast but unsafe one (for arguments validated during static analysis). So we need to weigh the pros and cons.