Migrate to new activity result API

[equeim]

No description provided.

[QuantumBadger]

Thanks @equeim -- just a heads-up that I'll be merging the 2024-06-new-gallery branch into master within the next few days, so it would be great if these changes could be rebased onto that branch please.

[equeim]

Rebased on master.

[QuantumBadger]

Thank you!

[QuantumBadger]

Sorry for the delay in reviewing this.

I've done some testing, and this crashed for me while trying to save an image link in a comment:

java.lang.IllegalStateException: LifecycleOwner org.quantumbadger.redreader.activities.CommentListingActivity@a89016a is attempting to register while current state is RESUMED. LifecycleOwners must call register before they are STARTED.
at androidx.activity.result.ActivityResultRegistry.register(ActivityResultRegistry.java:121)
at androidx.activity.ComponentActivity.registerForActivityResult(ComponentActivity.java:885)
at androidx.activity.ComponentActivity.registerForActivityResult(ComponentActivity.java:894)
at org.quantumbadger.redreader.common.FileUtils.createSAFDocumentWithIntent(FileUtils.java:345)
at org.quantumbadger.redreader.common.FileUtils.lambda$saveImageAtUri$5(FileUtils.java:400)
at org.quantumbadger.redreader.common.FileUtils$$ExternalSyntheticLambda7.onSuccess(D8$$SyntheticClass:0)
at org.quantumbadger.redreader.common.FileUtils$2$1.onCacheFileWritten(FileUtils.java:640)
at org.quantumbadger.redreader.cache.CacheRequest.notifyCacheFileWritten(CacheRequest.java:298)
at org.quantumbadger.redreader.cache.CacheManager$RequestHandlerThread$1.run(CacheManager.java:744)
at org.quantumbadger.redreader.common.PrioritisedCachedThreadPool$Executor.run(PrioritisedCachedThreadPool.java:103)
at java.lang.Thread.run(Thread.java:923)