Deprecate and hide @Nullable, @NonNull annotations to avoid name clashes with jspecify

Currently, `org.jetbrains.kotlin:kotlin-stdlib:2.2.21` depends on `org.jetbrains:annotations`, so it brings `org.jetbrains.annotations.Nullable` to IDE autocomplete.

The ecosystem moves towards https://jspecify.dev/, so it would be nice if you could deprecate and hide `@Nullable` and `@NonNull` annotations.

Deprecation is straightforward: `@Deprecated` + release announcement.
Hiding would probably involve adding `ACC_SYNTHETIC` modifier after the compilation. It would still keep the class in the bytecode, so the old libraries would still work fine in the runtime, while the new clients would need to move to a different nullability annotations.
An alternative option could be to rewrite `@Nullable` annotation in Kotlin and use `@Deprecated(level = HIDDEN)`