feat: add the ability override extended interfaces, fixes HTMLElement onerror type

[cosmic-pixel-painter]

Description

This PR started as a fix for this TypeScript issue. To handle it, I needed to update how the emitter.ts handled generating interfaces.

The HTMLElement extends the GlobalEventHandlers.onerror property. I didn't want to blow away the whole type to handle this fix. I thought something more flexible would make fixes like this scalable.
I was looking at

const extendConflictsBaseTypes: Record<
  string,
  { extendType: string[]; memberNames: Set<string> }
> = {
  HTMLCollection: {
    extendType: ["HTMLFormControlsCollection"],
    memberNames: new Set(["namedItem"]),
  },
};

and thought that is where I could add the flexibity by adding a new key but I didn't want to break any existing functionality or misuse a type.

I added

const extendConflictsInterfaces: Record<
  string,
  { overrideMap: Record<string, string> }
> = {
  HTMLElement: {
    overrideMap: {
      GlobalEventHandlers: 'Omit<GlobalEventHandlers, "onerror">',
    },
  },
};

It allows you to define a type and override its interfaces when unique cases arise.

I've included fixes for HTMLElement and SvgElement. If these changes are approved but we'd like to split the PR up into discrete chunks that's no problem. I'm also open to other approaches so if there's a more obvious place to bring this in I can update the PR.

[github-actions]

Thanks for the PR!

This section of the codebase is owned by @saschanaz - if they write a comment saying "LGTM" then it will be merged.

[cosmic-pixel-painter]

@microsoft-github-policy-service agree

[saschanaz]

Where did UIEvent come from? Looks like a bug.

I think we should instead add an interface that inherits from GlobalEventHandlers (maybe name it DocumentOrElementEventHandlers or such) and make others inherit from it, that way we don't need to repeat onerror for each interface and no need to touch emitter logic (as overridingTypes.jsonc should be able to handle it).

[cosmic-pixel-painter]

That's a good call. Let me see what I can do there.

I have a question out curiosity: is there ever a situation where using something like that omit in the emitter would be necessary or was I misunderstanding some of the architecture of overridingTypes.jsonc?