FIR: Make LHS of FirVariableAssignment a FirExpression

This way references can even be resolved for erroneous assignments
(e.g. function call, if expression, ... on LHS)

^KT-54648 Fixed

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

@@ -243,7 +243,7 @@ class FirVisualizer(private val firFile: FirFile) : BaseRenderer() {
                 }
                 else -> {
                     expression.allOfTypeWithLocalReplace<FirFunctionCall>(operation) { this.calleeReference.name.asString() }
-                        ?: expression.firstOfTypeWithLocalReplace<FirVariableAssignment>(operation) { this.lValue.toString() }
+                        ?: expression.firstOfTypeWithLocalReplace<FirVariableAssignment>(operation) { this.calleeReference.toString() }
                     super.visitBinaryExpression(expression)
                 }
             }