Add dozens of new integration tests to the GDScript test suite

This also ignores `.out` files in the file format static checks.

modules/gdscript/tests/scripts/parser/features/truthiness.gd

@@ -0,0 +1,30 @@
+func test():
+	# The assertions below should all evaluate to `true` for this test to pass.
+	assert(true)
+	assert(not false)
+	assert(500)
+	assert(not 0)
+	assert(500.5)
+	assert(not 0.0)
+	assert("non-empty string")
+	assert(["non-empty array"])
+	assert({"non-empty": "dictionary"})
+	assert(Vector2(1, 0))
+	assert(Vector2i(-1, -1))
+	assert(Vector3(0, 0, 0.0001))
+	assert(Vector3i(0, 0, 10000))
+
+	# Zero position is `true` only if the Rect2's size is non-zero.
+	assert(Rect2(0, 0, 0, 1))
+
+	# Zero size is `true` only if the position is non-zero.
+	assert(Rect2(1, 1, 0, 0))
+
+	# Zero position is `true` only if the Rect2's size is non-zero.
+	assert(Rect2i(0, 0, 0, 1))
+
+	# Zero size is `true` only if the position is non-zero.
+	assert(Rect2i(1, 1, 0, 0))
+
+	# A fully black color is only truthy if its alpha component is not equal to `1`.
+	assert(Color(0, 0, 0, 0.5))