Screen capture: Call interactor for fullscreen screenshots

Both the ScreenCaptureViewModel and ScreenshotInteractors are setup. The
next step is to have the view model call the interactor when the user
initiates a fullscreen screenshot.

Bug: 427476661
Test: atest ScreenCaptureViewModelTest
Flag: com.android.systemui.desktop_screen_capture
Change-Id: I0be4fefe40c7419e9bda2243b5be21c0b63ed13d