Replace RxJava3 code with coroutines (#4290)

This pull request removes the remaining RxJava code and replaces it with
coroutine-equivalent implementations.

- Remove all duplicate methods in `MastodonApi`:
- Methods returning a RxJava `Single` have been replaced by suspending
methods returning a `NetworkResult` in order to be consistent with the
new code.
- _sync_/_async_ method variants are replaced with the _async_ version
only (suspending method), and `runBlocking{}` is used to make the async
variant synchronous.
- Create a custom coroutine-based implementation of `Single` for usage
in Java code where launching a coroutine is not possible. This class can
be deleted after remaining Java code has been converted to Kotlin.
- `NotificationsFragment.java` can subscribe to `EventHub` events by
calling the new lifecycle-aware `EventHub.subscribe()` method. This
allows using the `SharedFlow` as single source of truth for all events.
- Rx Autodispose is replaced by `lifecycleScope.launch()` which will
automatically cancel the coroutine when the Fragment view/Activity is
destroyed.
- Background work is launched in the existing injectable
`externalScope`, since using `GlobalScope` is discouraged.
`externalScope` has been changed to be a `@Singleton` and to use the
main dispatcher by default.
- Transform `ShareShortcutHelper` to an injectable utility class so it
can use the application `Context` and `externalScope` as provided
dependencies to launch a background coroutine.
- Implement a custom Glide extension method
`RequestBuilder.submitAsync()` to do the same thing as
`RequestBuilder.submit().get()` in a non-blocking way. This way there is
no need to switch to a background dispatcher and block a background
thread, and cancellation is supported out-of-the-box.
- An utility method `Fragment.updateRelativeTimePeriodically()` has been
added to remove duplicate logic in `TimelineFragment` and
`NotificationsFragment`, and the logic is now implemented using a simple
coroutine instead of `Observable.interval()`. Note that the periodic
update now happens between onStart and onStop instead of between
onResume and onPause, since the Fragment is not interactive but is still
visible in the started state.
- Rewrite `BottomSheetActivityTest` using coroutines tests.
- Remove all RxJava library dependencies.

app/src/main/java/com/keylesspalace/tusky/MainActivity.kt

@@ -91,6 +91,7 @@ import com.keylesspalace.tusky.components.trending.TrendingActivity
 import com.keylesspalace.tusky.databinding.ActivityMainBinding
 import com.keylesspalace.tusky.db.AccountEntity
 import com.keylesspalace.tusky.db.DraftsAlert
+import com.keylesspalace.tusky.di.ApplicationScope
 import com.keylesspalace.tusky.entity.Account
 import com.keylesspalace.tusky.entity.Notification
 import com.keylesspalace.tusky.entity.Status
@@ -102,6 +103,7 @@ import com.keylesspalace.tusky.pager.MainPagerAdapter
 import com.keylesspalace.tusky.settings.PrefKeys
 import com.keylesspalace.tusky.usecase.DeveloperToolsUseCase
 import com.keylesspalace.tusky.usecase.LogoutUsecase
+import com.keylesspalace.tusky.util.ShareShortcutHelper
 import com.keylesspalace.tusky.util.deleteStaleCachedMedia
 import com.keylesspalace.tusky.util.emojify
 import com.keylesspalace.tusky.util.getDimension
@@ -111,7 +113,6 @@ import com.keylesspalace.tusky.util.show
 import com.keylesspalace.tusky.util.startActivityWithSlideInAnimation
 import com.keylesspalace.tusky.util.supportsOverridingActivityTransitions
 import com.keylesspalace.tusky.util.unsafeLazy
-import com.keylesspalace.tusky.util.updateShortcut
 import com.keylesspalace.tusky.util.viewBinding
 import com.mikepenz.iconics.IconicsDrawable
 import com.mikepenz.iconics.typeface.library.googlematerial.GoogleMaterial
@@ -143,8 +144,8 @@ import com.mikepenz.materialdrawer.widget.AccountHeaderView
 import dagger.android.DispatchingAndroidInjector
 import dagger.android.HasAndroidInjector
 import de.c1710.filemojicompat_ui.helpers.EMOJI_PREFERENCE
-import io.reactivex.rxjava3.schedulers.Schedulers
 import javax.inject.Inject
+import kotlinx.coroutines.CoroutineScope
 import kotlinx.coroutines.Dispatchers
 import kotlinx.coroutines.launch
 
@@ -167,6 +168,13 @@ class MainActivity : BottomSheetActivity(), ActionButtonActivity, HasAndroidInje
     @Inject
     lateinit var developerToolsUseCase: DeveloperToolsUseCase
 
+    @Inject
+    lateinit var shareShortcutHelper: ShareShortcutHelper
+
+    @Inject
+    @ApplicationScope
+    lateinit var externalScope: CoroutineScope
+
     private val binding by viewBinding(ActivityMainBinding::inflate)
 
     private lateinit var header: AccountHeaderView
@@ -382,7 +390,7 @@ class MainActivity : BottomSheetActivity(), ActionButtonActivity, HasAndroidInje
             }
         }
 
-        Schedulers.io().scheduleDirect {
+        externalScope.launch(Dispatchers.IO) {
             // Flush old media that was cached for sharing
             deleteStaleCachedMedia(applicationContext.getExternalFilesDir("Tusky"))
         }
@@ -1056,7 +1064,7 @@ class MainActivity : BottomSheetActivity(), ActionButtonActivity, HasAndroidInje
         }
 
         updateProfiles()
-        updateShortcut(this, accountManager.activeAccount!!)
+        shareShortcutHelper.updateShortcut(accountManager.activeAccount!!)
     }
 
     @SuppressLint("CheckResult")