Increment operator (++) not reactive on auto-subscription variable

[abastardi]

import { writable } from 'svelte/store';

let count1 = 0;
const count2 = writable(0);

function increment1() {
    count1++;
}

function increment2() {
    $count2++;
}

Above, count++ is reactive, but $count++ (a store auto-subscription variable) is not.

The generated code is:

function increment2() {
    $count2++;
}

but should be:

function increment2() {
    $count2++; count2.set($count2);
}

This was confirmed as a bug on Discord.

REPL reproduction

[Conduitry]

My current idea is to fold the UpdateExpression branch into the AssignmentExpression branch here except to use node.argument instead of node.left when it's an update expression. This appears to fix this issue, but it causing one other test failure I haven't investigated yet.