GDScript: Add support for variadic functions

modules/gdscript/tests/scripts/analyzer/errors/variadic_functions.gd

@@ -0,0 +1,22 @@
+class A:
+	func f1(x: int, ...args: Array) -> void:
+		prints(x, args)
+
+	func f2(x: int, ...args: Array) -> void:
+		prints(x, args)
+
+class B extends A:
+	func f1(x: int, y: int, ...args: Array) -> void:
+		prints(x, y, args)
+
+	func f2(x: int) -> void:
+		print(x)
+
+func g(...args: int):
+	pass
+
+func h(...args: Array[int]):
+	pass
+
+func test():
+	pass

modules/gdscript/tests/scripts/analyzer/errors/variadic_functions.out

@@ -0,0 +1,5 @@
+GDTEST_ANALYZER_ERROR
+>> ERROR at line 15: The rest parameter type must be "Array", but "int" is specified.
+>> ERROR at line 18: Typed arrays are currently not supported for the rest parameter.
+>> ERROR at line 9: The function signature doesn't match the parent. Parent signature is "f1(int, ...) -> void".
+>> ERROR at line 12: The function signature doesn't match the parent. Parent signature is "f2(int, ...) -> void".