Implement a @nonnull JSDoc tag

[DanielRosenwasser]

Fixes #23405.

[typescript-bot]

Looks like you're introducing a change to the public API surface area. If this includes breaking changes, please document them on our wiki's API Breaking Changes page.

Also, please make sure @DanielRosenwasser and @RyanCavanaugh are aware of the changes, just as a heads up.

[NemoStein]

TS 5.5 beta is released, but this isn't merged yet... Are there any plans to ship this with 5.5 or will it be pushd forward?

[codenomnom]

Any news on this one? It's been a while...

[tats-u]

@sandersn You should leave a review to other members if you are too busy to review it.
About 1 year has been passed.

[aweebit]

@nonnull is a pretty bad name for this, makes it feel like it's only about null, and not undefined.

@nonnullable is better as it corresponds to the NonNullable utility type's name.

@nonnullish with nullish as in the nullish coalescing operator meaning exactly that, the null and undefined values, is also a good alternative.

But my favorite option is actually /** @type {!} */.

[louwers]

I like nonnullable better, it is a bit more verbose, but JSDoc does not shy away from some verbosity.