Revert "Revert "Bug 971546 - [System2] Instantiable Screenshot" for possibly breaking gaia-ui tests on TBPL"

This reverts commit 60e9eb1aa68a27fa21e75264e52409aa5a2b4cc4.
Merge pull request #17376 from timdream/system2-screenshot-land

Bug 971546 - [System2] Instantiable Screenshot, r=alive