Fix assembleAndroidTest builds

[mrbrentkelly]

Overview

Fixes an issue when building and running instrumented tests (e.g. Detox) for a React Native project on Android, the following build error was occurring:

> Task :react-native-push-notification:mergeExtDexDebugAndroidTest FAILED
FAILURE: Build failed with an exception.
* What went wrong:
Execution failed for task ':react-native-push-notification:mergeExtDexDebugAndroidTest'.
> Could not resolve all files for configuration ':react-native-push-notification:debugAndroidTestRuntimeClasspath'.
   > Failed to transform firebase-datatransport-18.0.0.aar (com.google.firebase:firebase-datatransport:18.0.0) to match attributes {artifactType=android-dex, dexing-enable-desugaring=false, dexing-is-debuggable=true, dexing-min-sdk=23, org.gradle.status=release, org.gradle.usage=java-runtime}.
      > Execution failed for DexingNoClasspathTransform: C:\Users\some-user\.gradle\caches\transforms-2\files-2.1\4d61182c30ea6157b57a4d6f697f3dae\firebase-datatransport-18.0.0-runtime.jar.
         > Error while dexing.
           The dependency contains Java 8 bytecode. Please enable desugaring by adding the following to build.gradle
           android {
               compileOptions {
                   sourceCompatibility 1.8
                   targetCompatibility 1.8
               }
           }
           See https://developer.android.com/studio/write/java8-support.html for details. Alternatively, increase the minSdkVersion to 26 or above.

If an Android library uses Java 8 language features then it must declare compileOptions in its build.gradle.

...each module that uses Java 8 language features (either in its source code or through dependencies), update the module's build.gradle file, as shown below:

https://developer.android.com/studio/write/java8-support#supported_features

Fix is simply to add Java 8 compileOptions to the build.gradle. I've seen and fixed similar issues in other projects as well:

negativetwelve/react-native-ux-cam#104
react-native-netinfo/react-native-netinfo#466
snowplow/snowplow-react-native-tracker#117

Test Plan

Made the change locally in my projects node_modules, then rebuilt the app, and it was successful 🎉 .

[Dallas62]

Thanks for your contribution !
This will be release in the next version