GDScript: Add return type covariance and parameter type contravariance

modules/gdscript/tests/scripts/analyzer/features/function_param_type_contravariance.gd

@@ -0,0 +1,20 @@
+class A:
+	func int_to_variant(_p: int): pass
+	func node_to_variant(_p: Node): pass
+	func node_2d_to_node(_p: Node2D): pass
+
+	func variant_to_untyped(_p: Variant): pass
+	func int_to_untyped(_p: int): pass
+	func node_to_untyped(_p: Node): pass
+
+class B extends A:
+	func int_to_variant(_p: Variant): pass
+	func node_to_variant(_p: Variant): pass
+	func node_2d_to_node(_p: Node): pass
+
+	func variant_to_untyped(_p): pass
+	func int_to_untyped(_p): pass
+	func node_to_untyped(_p): pass
+
+func test():
+	pass

modules/gdscript/tests/scripts/analyzer/features/function_param_type_contravariance.out

@@ -0,0 +1 @@
+GDTEST_OK

modules/gdscript/tests/scripts/analyzer/features/function_return_type_covariance.gd

@@ -0,0 +1,32 @@
+class A:
+	func variant_to_int() -> Variant: return 0
+	func variant_to_node() -> Variant: return null
+	func node_to_node_2d() -> Node: return null
+
+	func untyped_to_void(): pass
+	func untyped_to_variant(): pass
+	func untyped_to_int(): pass
+	func untyped_to_node(): pass
+
+	func void_to_untyped() -> void: pass
+	func variant_to_untyped() -> Variant: return null
+	func int_to_untyped() -> int: return 0
+	func node_to_untyped() -> Node: return null
+
+class B extends A:
+	func variant_to_int() -> int: return 0
+	func variant_to_node() -> Node: return null
+	func node_to_node_2d() -> Node2D: return null
+
+	func untyped_to_void() -> void: pass
+	func untyped_to_variant() -> Variant: return null
+	func untyped_to_int() -> int: return 0
+	func untyped_to_node() -> Node: return null
+
+	func void_to_untyped(): pass
+	func variant_to_untyped(): pass
+	func int_to_untyped(): pass
+	func node_to_untyped(): pass
+
+func test():
+	pass

modules/gdscript/tests/scripts/analyzer/features/function_return_type_covariance.out

@@ -0,0 +1 @@
+GDTEST_OK