Send onCreatePredictionSession, sortAppTargets, requestPredictionUpdate

immediately instead of sending them to main thread Looper queue of
ChooserActivity.

These methods are relatively latency-sensitive. When main thread Looper queue has many backlogs, it takes long time
to dispatch requests.

Bug: 155551642
Test: atest CtsSharesheetTestCases:android.sharesheet.cts.CtsSharesheetDeviceTest
Test: manually test on the device
Change-Id: I7d00e49c6a30fec478e620bc98180d379f801fc8