Set correct IR origins for inc/dec operations

NB: in order to produce correct IR origins, the source element kinds for
some FIR elements has been changed. As a side effect, mapping PSI to FIR
slightly changed: namely, for `a[b]++`, `a[b]` used to be mapped on
`set` call or callable reference, but now it is mapped on `get` call.

^KT-61891: Fixed
^KT-64387: Fixed

compiler/testData/ir/irText/expressions/kt36956.kt

@@ -1,3 +1,4 @@
+// FIR_IDENTICAL
 class A<T>(private val value: T) {
     operator fun get(i: Int) = value
     operator fun set(i: Int, v: T) {}