Add JPMS module name

[jodastephen]

Move to the correct pom.xml.

Fixes #2920
Commit 9feba7c of #2846 placed the Automatic-Module-Name declaration in the wrongpom.xml. As such, Guava still isn't a valid module, which blocks a whole heap of projects from declaring module-info.java.

Feel free to make a separate change rather than merging this PR to satisfy any IP rules.

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[jbduncan]

@jodastephen By my understanding, if you just sign the Google CLA, then that should be enough to allow this PR to be considered for merging.

[jodastephen]

I signed it!

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CLAs look good, thanks!

[cpovirk]

Thanks. Any opinion on whether we should set an Automatic-Module-Name for our guava-testlib test utilities? They're much, much less heavily used, but maybe we might as well? Or maybe it's not worth worrying about modules for code that runs only in tests, since it sounds like there might not be a good story yet for running most tests with modules on?

[jodastephen]

As it stands, I don't think its clear how test libraries will operate with modules - I suspect that modules don't really apply there. If runtime code might depend on testlib then of course it should have a module name.

[cpovirk]

Thanks.