Tor Browser on Android is crashing on newer Android devices (>= Android N) by file download

This is already patched upstream in FF62, but the backport is not-small. Maybe we can get away with a smaller patch that solves the main problem.

Summary: In #27701 (moved) we solved the bug where torbutton prevents downloading a file on Android. In #28051 (moved) we solved the problem where notifications weren't working on newer versions of Android.

Now we have a problem that on newer versions of Android, the runtime prevents "leaking" file URIs from one app to another. In particular, this is happening when Tor Browser is downloading a file, the browser creates a notification with the URI of the local destination file embedded in it.

This results in an exception stacktrace like:

D AndroidRuntime: Shutting down VM
E AndroidRuntime: FATAL EXCEPTION: main
E AndroidRuntime: Process: org.torproject.torbrowser_alpha, PID: 18167
E AndroidRuntime: android.os.FileUriExposedException: file:///storage/emulated/0/Download/tor-browser-8.5a5-android-armv7.apk exposed beyond app through Intent.getData()
E AndroidRuntime:        at android.os.StrictMode.onFileUriExposed(StrictMode.java:1960)
E AndroidRuntime:        at android.net.Uri.checkFileUriExposed(Uri.java:2356)
E AndroidRuntime:        at android.content.Intent.prepareToLeaveProcess(Intent.java:9881)
E AndroidRuntime:        at android.content.Intent.prepareToLeaveProcess(Intent.java:9835)
E AndroidRuntime:        at android.app.PendingIntent.getActivity(PendingIntent.java:342)
E AndroidRuntime:        at android.app.PendingIntent.getActivity(PendingIntent.java:304)
E AndroidRuntime:        at org.mozilla.gecko.notifications.NotificationHelper.showNotification(NotificationHelper.java:298)
E AndroidRuntime:        at org.mozilla.gecko.notifications.NotificationHelper.handleMessage(NotificationHelper.java:120)
E AndroidRuntime:        at org.mozilla.gecko.EventDispatcher$2.run(EventDispatcher.java:337)
E AndroidRuntime:        at android.os.Handler.handleCallback(Handler.java:790)
E AndroidRuntime:        at android.os.Handler.dispatchMessage(Handler.java:99)
E AndroidRuntime:        at android.os.Looper.loop(Looper.java:164)
E AndroidRuntime:        at android.app.ActivityThread.main(ActivityThread.java:6494)
E AndroidRuntime:        at java.lang.reflect.Method.invoke(Native Method)
E AndroidRuntime:        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:438)
E AndroidRuntime:        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:807)

This was patched upstream: https://bugzilla.mozilla.org/show_bug.cgi?id=1450449

Crash report: https://bugzilla.mozilla.org/show_bug.cgi?id=1476681