Android: Enable all warnings on javac for user code too

In addtion to 1cf03c974c433b7a5330b56bd9e519287fce6f7f we should also
enable all warnings in the template as a recommendation for users.

Change-Id: If60a3d9f3c1fd97b49ec7513f781bdfe1775d9d4
Reviewed-by: Assam Boudjelthia <assam.boudjelthia@qt.io>
(cherry picked from commit 577f9ebfe6e6d7f5453fae7850055ded32b5d09f)
Reviewed-by: Qt Cherry-pick Bot <cherrypick_bot@qt-project.org>

src/android/templates/build.gradle

@@ -58,6 +58,7 @@ android {
 
     tasks.withType(JavaCompile) {
         options.incremental = true
+        options.compilerArgs += ['-Xlint:all']
     }
 
     compileOptions {