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

analysis/low-level-api-fir/testData/getOrBuildFir/calls/incWithArrayAccessConvention.txt

@@ -1,6 +1,6 @@
 KT element: KtPostfixExpression
 FIR element: FirFunctionCallImpl
-FIR source kind: DesugaredIncrementOrDecrement
+FIR source kind: DesugaredPostfixInc
 
 FIR element rendered:
 R|<local>/<array>|.R|SubstitutionOverride</MyMap.set: R|kotlin/Unit|>|(R|<local>/<index_0>|, R|<local>/<unary>|.R|/A.inc|())