c0bf3d3c94
There's a fair number of event listeners in the editor-code that we're currently removing "manually", by keeping references to their event handler functions. This was necessary since we have a "global" `AbortController` that applies to all event listeners used in the editor-code, however it's now possible to combine multiple `AbortSignal`s; please see https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal/any_static Since this functionality is [fairly new](https://developer.mozilla.org/en-US/docs/Web/API/AbortSignal/any_static#browser_compatibility) the viewer will check that `AbortSignal.any()` is available before enabling the editing-functionality. (It should hopefully be fairly straightforward, famous last words, for users to implement a polyfill to allow editing in older browsers.) Finally, this patch also adds checks and test-only asserts to ensure that we don't add duplicate event listeners in various editor-code.