Migrate from `javax` to `jakarta`

[Harmelodic]

There's a bunch of usages of javax in this library.

ALL of them related to javax.annotation.

Usage of javax.annotation:javax.annotation-api in this repo results in it being transitively passed to all consumers of the google-cloud-pubsub library, including com.google.cloud:spring-cloud-gcp-pubsub and beyond.

It would be good to modernize this library to have it use the jakarta.annotation instead.

[michaelpri10]

The usage of javax is in the auto-generated layer of our library, which is controlled by the underlying Cloud Java. There is a tracking issue for this in that repository (googleapis/sdk-platform-java#1938), so closing this as a duplicate of that issue.

[Harmelodic]

Sure, but there's also other javax usages in this library that aren't to do with generated code.

https://github.com/search?q=repo%3Agoogleapis%2Fjava-pubsub+javax+NOT+javax.annotation.Generated&type=code

These (at time of writing) are two instances of Nullable and usages of the javax.annotation-api package in 2 Maven profiles.

Can those be migrated?

[michaelpri10]

Re-opening to look into whether we can migrate Nullable instances to use jakarta in this library.

[Harmelodic]

Re-opening to look into whether we can migrate Nullable instances to use jakarta in this library.

Link to jakarta.annotation.Nullable.