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

compiler/visualizer/render-fir/src/org/jetbrains/kotlin/compiler/visualizer/FirVisualizer.kt

@@ -742,7 +742,7 @@ class FirVisualizer(private val firFile: FirFile) : BaseRenderer() {
         override fun visitSafeCallExpression(safeCallExpression: FirSafeCallExpression, data: StringBuilder) {
             safeCallExpression.receiver.accept(this, data)
             data.append("?.{ ")
-            safeCallExpression.regularQualifiedAccess.accept(this, data)
+            safeCallExpression.selector.accept(this, data)
             data.append(" }")
         }