Recognize that compareUnsigned is safe on Byte and Short.

[cpovirk]

They have been always desugared since
https://r8.googlesource.com/r8/+/4b8c252dbd34d0b8d1d5defe7bbe5da288eed677,
which came shortly after support for Long and Integer,
https://r8.googlesource.com/r8/+/62ef970fea988efa2bbfc81e68d1072d5ab930d7,
which is already recognized by Gummy Bears.

[cpovirk]

This should perhaps be more of a feature request than a PR, as I'm not at all confident that I've edited the right place :) But I figured I'd attempt it as a PR in case it does turn out to be this easy.

[cpovirk]

Ha, and as soon as I pushed this, I looked at my latest testing results, and I realized that the actual problem was a failure in our JVM Animal Sniffer check, as this API doesn't exist until Java 9 (and we check for compatibility with Java 8)!

It's entirely possible that Gummy Bears already recognizes this under Android; my testing just didn't actually get that far, and I misread the error message.

I'll test some more and then let you know what I find.

[cpovirk]

OK, my mistake on the JVM side aside, I do still think that these APIs are always desugared, and I now have some evidence that this PR makes them be recognized as such:

Before:

[INFO] --- animal-sniffer:1.23:check (check-java-version-compatibility) @ guava ---
[INFO] Checking unresolved references to com.toasttab.android:gummy-bears-api-21:0.8.0
[ERROR] /usr/local/google/home/cpovirk/tmp.49wlVCLfVo/git/android/guava/src/com/google/common/primitives/UnsignedBytes.java:127: Undefined reference: int Byte.compareUnsigned(byte, byte)

After:

[INFO] --- animal-sniffer:1.23:check (check-java-version-compatibility) @ guava ---
[INFO] Checking unresolved references to com.toasttab.android:gummy-bears-api-21:0.8.1-SNAPSHOT

Now, in our particular use case, it's probably actually safer for us not to tell Animal Sniffer that, since we want our Android code to also work under a Java 8 JVM :) But I think this PR makes sense for testing actual Android compatibility. Feel free to merge or close it, as you prefer.

[ogolberg]

Thanks