Motivation: We can't publish to the Play Store with a targetSdkVersion < 31
The new targetSdk required two changes:
* Specifying when activities, services and receivers should be exported or
not to other apps. For the ones I wasn't sure of what we want, I made
them exported to not break something.
* Specifying when a PendingIntent should be mutable or immutable. I made
them all mutable for now.
Summary: Gradle is automatically configured by Android Studio. However, the project is troublesome to build when using other tools. Per https://docs.gradle.org/current/userguide/gradle_wrapper.html#sec:adding_wrapper, the files added by this patch ought to be included in the repository
Test Plan: After applying this diff, it should be possible to clone a fresh repository and run ./gradlew build, resulting in an .apk in ./build/outputs/apk/*/
Reviewers: #kde_connect, nicolasfella
Reviewed By: #kde_connect, nicolasfella
Subscribers: kdeconnect
Tags: #kde_connect
Differential Revision: https://phabricator.kde.org/D16439
