add tests for expr_optional_cast generation

tests/behavior/success/optional_cast.bz

@@ -0,0 +1,30 @@
+import resource;
+
+function test(##value)
+{
+	let _: ?##auto = __forward value;
+}
+
+function foo()
+{}
+
+function main()
+{
+	test(42u8);
+	test(42);
+	test(42i64);
+
+	let i = 0;
+	test(&i);
+
+	test(foo);
+
+	let func = foo;
+	test(func);
+
+	let i = 0;
+	test(i);
+
+	test(resource_t());
+	test(complex_resource_t());
+}