fix(44448): Non-optional but undefined delete under exactOptionalPropertyTypes

[a-tarasyuk]

Fixes #44448

[DanielRosenwasser]

You may need to rewrite a few tests since this option is going to be renamed and removed from --strict.

[a-tarasyuk]

@DanielRosenwasser Do you mean to use strictOptionalProperties in order to fix it after rename?

[DanielRosenwasser]

Yeah, and tests that assume strict will toggle the option will change in their behavior.

[mtreder]

I expected the following to be correct code, but it is generating an error:

declare const obj: {definitelyHereMaybeUndefined?: number};

delete obj.definitelyHereMaybeUndefined;

Playground Example

EDIT: The copied link doesn't seem to preserve the exactOptionalPropertyTypes flag.