Screen record user switching fixes

Allow opening the dialog in all users
Stop recording when the user changes
Post notifications in the correct user

Still some issues with tile state and status bar but those require more
work to coordinate across users, so may not make it into R
(related bug: b/158004991)

Fixes: 147921212
Bug: 148955577
Test: manual
Test: atest ScreenRecordTileTest
Test: atest com.android.systemui.screenrecord
Change-Id: Idf10931c5ddf3079b903708824fae11135169c1b