Upgrade Gradle to 7.2 and Android Gradle plugin to 4.2.

The older versions of the plugin caused problems building with newer
NDK versions due to a lack of MIPS support.

This also required upgrading to a version of Gradle that knows about
the Google Maven repository.

wa/workloads/gmail/uiauto/app/build.gradle

@@ -20,7 +20,7 @@ android {
         }
         applicationVariants.all { variant ->
             variant.outputs.each { output ->
-                output.outputFile = file("$project.buildDir/apk/${packageName}.apk")
+                output.outputFileName = "${packageName}.apk"
             }
         }
     }