GDScript: Allow using self in lambdas

modules/gdscript/tests/scripts/runtime/features/lambda_use_self.gd

@@ -0,0 +1,23 @@
+var member = "foo"
+
+func bar():
+	print("bar")
+
+func test():
+	var lambda1 = func():
+		print(member)
+	lambda1.call()
+
+	var lambda2 = func():
+		var nested = func():
+			print(member)
+		nested.call()
+	lambda2.call()
+
+	var lambda3 = func():
+		bar()
+	lambda3.call()
+
+	var lambda4 = func():
+		return self
+	print(lambda4.call() == self)

modules/gdscript/tests/scripts/runtime/features/lambda_use_self.out

@@ -0,0 +1,5 @@
+GDTEST_OK
+foo
+foo
+bar
+true