FIR: Allow selector of safe calls to be a FirStatement

It's necessary to allow a?.b += v be interpreted as a?.(b += v)
But currently FirAssignmentOperatorStatement is not FirQualifiedAccess

^KT-41034 In Progress

analysis/analysis-api-fir/src/org/jetbrains/kotlin/analysis/api/fir/components/KtFirCallResolver.kt

@@ -155,7 +155,7 @@ internal class KtFirCallResolver(
             )
             // FIR does not resolve to a symbol for equality calls.
             is FirEqualityOperatorCall -> toKtCallInfo(psi)
-            is FirSafeCallExpression -> regularQualifiedAccess.toKtCallInfo(
+            is FirSafeCallExpression -> selector.toKtCallInfo(
                 psi,
                 resolveCalleeExpressionOfFunctionCall,
                 resolveFragmentOfCall