Add static type checks in the parser

- Resolve types for all identifiers.
- Error when identifier is not found.
- Match return type and error when not returning a value when it should.
- Check unreachable code (code after sure return).
- Match argument count and types for function calls.
- Determine if return type of function call matches the assignment.
- Do static type check with match statement when possible.
- Use type hints to determine export type.
- Check compatibility between type hint and explicit export type.

modules/gdscript/gdscript_function.cpp

@@ -1370,6 +1370,15 @@ int GDScriptFunction::get_default_argument_addr(int p_idx) const {
 	return default_arguments[p_idx];
 }
 
+GDScriptDataType GDScriptFunction::get_return_type() const {
+	return return_type;
+}
+
+GDScriptDataType GDScriptFunction::get_argument_type(int p_idx) const {
+	ERR_FAIL_INDEX_V(p_idx, argument_types.size(), GDScriptDataType());
+	return argument_types[p_idx];
+}
+
 StringName GDScriptFunction::get_name() const {
 
 	return name;