Check compatibility against the Android SDK (including [always-desuga…

…red APIs](https://github.com/open-toast/gummy-bears#android) but still not opt-in library desugaring) instead of the JDK.

Fixes #4005

RELNOTES=n/a
PiperOrigin-RevId: 584349750

android/pom.xml

@@ -180,15 +180,14 @@
             <annotations>com.google.common.collect.IgnoreJRERequirement,com.google.common.hash.IgnoreJRERequirement,com.google.common.io.IgnoreJRERequirement,com.google.common.reflect.IgnoreJRERequirement,com.google.common.testing.IgnoreJRERequirement</annotations>
             <checkTestClasses>true</checkTestClasses>
             <signature>
-              <groupId>org.codehaus.mojo.signature</groupId>
-              <artifactId>java16-sun</artifactId>
-              <version>1.10</version>
+              <groupId>com.toasttab.android</groupId>
+              <artifactId>gummy-bears-api-19</artifactId>
+              <version>0.6.1</version>
+              <!-- TODO(cpovirk): In principle, it would make sense to *also* test compatibility with JDK 1.8, since guava-android also has JRE users. -->
             </signature>
             <ignores>
-              <!-- Allow requireNonNull: Android desugaring rewrites it (so it's safe for us to use), and it's useful for null checks. Note that this line allows *all* methods from java.util.Objects. That's the best that we can do with the configuration options that Animal Sniffer offers. -->
-              <ignore>java.util.Objects</ignore>
-              <!-- Unsafe isn't part of the documented Java 6 API, but it is available.
-                   And in cases where it's not, we have fallbacks. -->
+              <!-- Unsafe isn't part of the documented Android API, but it is available.
+                   And in cases where it's not, we have fallbacks (except maybe Striped64 (b/307807965)?). -->
               <ignore>sun.misc.Unsafe</ignore>
             </ignores>
           </configuration>