Fix: correct Mocha overloads order

[JoshuaKGoldberg]

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• Provide a URL to documentation or source code which provides context for the suggested changes: Calling an overloaded function should resolve to best match, not first microsoft/TypeScript#48077
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Corrects function overloads for it and the like in Mocha so that the more specific async parameters come first per microsoft/TypeScript#48077 (comment) (thanks @MartinJohns!).

I tried switching to unions but hit test errors about this no longer being defined: https://github.com/DefinitelyTyped/DefinitelyTyped/runs/5394917747?check_suite_focus=true

Error: /home/runner/work/DefinitelyTyped/DefinitelyTyped/types/ember-mocha/ember-mocha-tests.ts:79:9
ERROR: 79:9    expect  TypeScript@4.7 compile error: 
'this' implicitly has type 'any' because it does not have a type annotation.
...

Throwing this PR up as a draft while there are test failures as reference for microsoft/TypeScript#48088.

[lo1tuma]

What if we would use a rest parameter with a discriminated union type instead of function overrides as a workaround?

For example:

type HookFunction = (...args: [Func|AsyncFunc] | [string, (Func|AsyncFunc)?]) => void;

[JoshuaKGoldberg]

Closing as this is no longer relevant to me 🙂 . Feel free to pick back up, anybody!