Update Java conventions so that projects creating jars from jars don't have to exclude duplicate LICENSE and NOTICE files

[wilkinsona]

The build creates a handful of jars from other jars. This results in duplicate LICENSE.txt and NOTICE.txt files as they come both from the original jar and our conventions that add them to each jar that's built.

[wilkinsona]

The first attempt at this caused #24131 so it needs to be reverted for now.

[dreis2211]

May I give this an attempt, @wilkinsona ?

[wilkinsona]

@dreis2211 That'd be great, thank you. As you can see above I had one attempt that fixed the duplicates but introduced another problem so perhaps use 1e10067 as an example of what not to do! I haven't had a chance to take another look.