[JVM_IR] Extend when to switch translation to deal with nested ors.

FIR translates:

```
when (x) {
  1, 2, 3 -> action
  else -> other_action
}
```

to an IR structure with nested ors:

```
if ((x == 1 || x == 2) || (x == 3)) action
else other_action
```

This change allows that to turn into switch instructions in the
JVM backend.

compiler/testData/codegen/bytecodeText/whenStringOptimization/nullability.kt

@@ -1,4 +1,3 @@
-// IGNORE_BACKEND_FIR: JVM_IR
 fun foo1(x : String?) : String {
     when (x) {
         "abc", "cde" -> return "abc_cde"