use jakarta.annotation to document nullability of APIs

[gavinking]

see #725

[gavinking]

Setting this to Draft mode because it's a source of conflicts with other open PRs.

[hantsy]

For my opinion, it is better to introduce a @NullMarked or NullUnmarked like JSpecify, or use jspecify to replace the current @Nullable and @Nonnull in jakarta annotation API.

The good is using @NullMarked like annotation on class or package, and assume all parameters/fields/method result default is non null, only need to mark the @Nullable field/results, or in reverse. This way is clearer to use Nullable/Nonnull mixing in the same APIs.

Another benefit from JSpecify is the support from IDE when coding or build tools at compile time.

See: https://jspecify.dev/