[Partial Screensharing] Update app selector (ChooserActivity) header

Updates title style (increases font size), adds an icon
and hides the drag handle for media projection app
selector activity which is based on ChooserActivity.

Bug: 235465652
Test: atest com.android.internal.app.ChooserActivityTest
Test: screenshot test in a follow-up CL
Change-Id: Ib717d3f7e6132d56e8344f4e06a12a64ee63457b