Cannot have a value called `ctx`

**Describe the bug**

Svelte gets terribly confused if you name a variable `ctx`.

**To Reproduce**

https://svelte.dev/repl/636dd36f255f499fa7ed04c3b1a0dc71?version=3.12.1

**Expected behavior**

Hello world

**Severity**

I'm just amazed it hasn't come up already

**Additional context**

Will be fixed by #3539. Just leaving this here to make sure I don't forget
