Pre-cache max unreserved player count on process startup.

This call was taking up to 20ms to run on the first time we would
load a conversation. Adding a post-render call to app launch reduces
this time to 0ms, as the data has been cached by the system. Doing
it on a background thread means we do not pay for it in TTFF.

app/src/main/java/org/thoughtcrime/securesms/ApplicationContext.java

@@ -214,6 +214,7 @@ public class ApplicationContext extends MultiDexApplication implements AppForegr
                             .addPostRender(GroupV2UpdateSelfProfileKeyJob::enqueueForGroupsIfNecessary)
                             .addPostRender(StoryOnboardingDownloadJob.Companion::enqueueIfNeeded)
                             .addPostRender(PnpInitializeDevicesJob::enqueueIfNecessary)
+                            .addPostRender(() -> ApplicationDependencies.getExoPlayerPool().getPoolStats().getMaxUnreserved())
                             .execute();
 
     Log.d(TAG, "onCreate() took " + (System.currentTimeMillis() - startTime) + " ms");