JVM IR: Check that we generate callable references in tests

compiler/testData/codegen/box/directInvokeOptimization/canary.kt

@@ -0,0 +1,8 @@
+// The direct invoke optimization silently broke several tests. This test exists to
+// ensure that we don't end up optimizing the indirect invokes that are present in the tests.
+private fun id(x: String) = x
+
+fun box() = { "O" }.let { it() } + ::id.let { it("K") }
+
+// CHECK_BYTECODE_TEXT
+// 2 Function[^.\n]*\.invoke