In FIR we desugar when with multiple conditions leading to same block
as tree of OR expressions
Given
```
when(some) {
"a", "b", "c" -> {}
else -> {}
}
```
actually desugared into
```
when(val <subj> = some) {
<subj> == "a" || <subj> == "b" || <subj> == "c" -> {}
else -> {}
}
```
There is a multiple ways of how we can organize such expressions in FIR
Previously it was just nesting-chain of OR expressions
While the most efficient way in terms of required stack depth is
a balanced tree
KT-53255
Simon Ogorodnik