Bug 964653 - (system-dialog) [Window Management] Implement System Dialog Window

(cherry picked from commit dcebc4a94b3177c8cee5dce1ed4cfa6acd41550c)

Conflicts:
	apps/system/js/bootstrap.js
	apps/system/js/layout_manager.js
	apps/system/test/unit/mock_layout_manager.js
Merge pull request #16703 from ian-liu/bubble_tea/system/bug964653_system_dialog_refactor

Bug 964653 - (system-dialog) [Window Management] Implement System Dialog Window, r=@alivedise
Bug 971458 - [System2] Instantiable AppWindowFactory