Detecting display size changes is not straightforward:
- from a DisplayListener, "display changed" events are received, but
this does not imply that the size has changed (it must be checked)
- on Android 14 (see e26bdb07a21493d096ea5c8cfd870fc5a3f015dc),
"display changed" events are not received on some versions, so as a
fallback, a RotationWatcher and a DisplayFoldListener are registered,
but unregistered as soon as a "display changed" event is actually
received, which means that the problem is fixed.
Extract a "display size monitor" to share the code between screen
capture and virtual display capture.
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