FIR IDE: Consolidate tests for AddExclExclFix in one directory.

I found these tests only _after_ the previous changes, so I needed to
merge and/or remove redundant tests.

idea/testData/quickfix/addExclExclCall/iterableDoesNotInheritIterableInterface.kt.after

@@ -0,0 +1,9 @@
+// "Add non-null asserted (!!) call" "true"
+class Some {
+    operator fun iterator(): Iterator<Int> = null!!
+}
+
+fun foo() {
+    val test: Some? = Some()
+    for (i in test!!) { }
+}