[FIR] Add some corner case tests for KT-64891

Note that there are some that K2
correctly supports, while K1 fails.

^KT-64891

compiler/testData/diagnostics/tests/expressionsInQaSelectorsWithElvis.kt

@@ -0,0 +1,6 @@
+// FIR_IDENTICAL
+// ISSUE: KT-64891
+
+fun test(a: (Int.() -> Int)?, b: Int.() -> Int) {
+    2.(a ?: b)()
+}