Screen Sharing: Replace ScreenShareTarget with ScreenCaptureTarget

Use dummy data 0 to create the target object. Also update the default
target to tab sharing.

BUG: b/443082217 b/442626685
Test: atest SystemUITests:com.android.systemui.screencapture.sharescreen
Flag: com.android.systemui.large_screen_sharing
Change-Id: I4dd0c795b75c0ebc4691a23d3db209246840d22c