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.
Otherwise some tools break (e.g. CheckMethodAdapter in ASM, used in generic
signature writer) because they expect class names to be Java identifiers.
Some tests fixed, some will be fixed in future commits
Mads Ager