KT-53255. Fix StackOverflow during IR verification from K2

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

compiler/testData/codegen/box/when/longCondition.kt

@@ -1,5 +1,4 @@
 // TARGET_BACKEND: JVM_IR
-// IGNORE_BACKEND_FIR: JVM_IR
 
 fun box(): String {
     return when ("foo") {