Emit @CanIgnoreReturnValue annotations on flatbuffer APIs.

[kluever]

[dbaileychess]

@paulovap Can you help with the kotlin issue?

[paulovap]

Hello @kluever, may I ask why is it necessary to add this dependency?

[dbaileychess]

I think linters complain that some methods have return values that are not used. This annotation marks that those values can be ignored safely, since the method had some other side affect.

[kluever]

Indeed. ~all of the Java classes / packages in flatbuffers should really be tagged with @CheckReturnValue as well, so external users of these APIs don't make coding mistakes (if they're using https://github.com/google/error-prone)

[dbaileychess]

@kluever can you rebase?

[dbaileychess]

@kluever could we move this forward again?