[Screen share] Update strings and icon in app chooser activity.

Bug: 352327853
Flag: NONE string changes
Test: Cast single app -> verify app chooser activity says "Choose app to
cast" and has cast icon
Test: Screen record single app -> verify app chooser activity says
"Choose app to record" and has red screen record icon
Test: Share single app -> verify app chooser activity says "Choose app
to share" and has share icon

Change-Id: I4fa96334ccfe6dda52f4e8ac3ac1fbca479e7f2e