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/warnings/standalone_expression.gd

@@ -0,0 +1,9 @@
+func test():
+	# The following statements should all be reported as standalone expressions:
+	"This is a standalone expression"
+	1234
+	0.0 + 0.0
+	Color(1, 1, 1)
+	Vector3.ZERO
+	[true, false]
+	float(125)