Ensure that MEDIA_PROJECTION_STATE_CANCELLED is only emitted when actually cancelling set up

Discovered that we were emiting an atom with MEDIA_PROJECTION_STATE_CANCELLED every time we transition from the Permission Dialog, even if it is an intended transition like to start capture or to open the app selector. Added a small boolean flag so now we only emit an atom with MEDIA_PROJECTION_STATE_CANCELLED when we are cancelling the media projection set up (i.e. pressing the cancel button or clicking away from the dialog)

Bug: 237527771
Flag: None
Test: atest CtsStatsdAtomHostTestCases:MediaProjectionAtomsTests
Test: atest ScreenRecordPermissionDialogDelegateTest
Change-Id: Idde4a9f609811e0fbb5f5a9fe0cca03b8451f2e3