Support a @nonnull/@nonnullable JSDoc assertion comment

[DanielRosenwasser]

This could be used in place of the non-null assertion operator, and solve #23403.

while (queue.length) {
    (/** @nonnull */ queue.pop())();
}

Related is #23217, which tracks definite assignment assertions.

[RyanCavanaugh]

@sandersn please add /** @nonnull */expr as JS sugar for (expr as NonNullable<typeof expr>) 🍻

[weswigham]

@RyanCavanaugh Or more appropriately as sugar for expr!, which is almost just sugar for (expr as NonNullable<typeof expr>), but also has fallback behavior if NonNullable doesn't exist.

[RyanCavanaugh]

That's the easier and more correct way to write it, yes 😝