Adds two UiEvent IDs for actions on long screenshots

After completing a long screenshot, and viewing the result:

SCREENSHOT_LONG_SCREEHSHOT_SAVE

 -  Logged when the "Save" button is tapped

SCREENSHOT_LONG_SCREENSHOT_EXIT

 - Logged then the "Cancel" button is tapped

Bug: 200295026
Test: manually, make statsd_testdrive && statsd_testdrive 90
Change-Id: Iba841287a31853685cfe2596f5a591b31c1166af