dataengines/mpris2: Delete Multiplexer when there is no player
When all players are closed, media player applet on the desktop still shows a track from the last player, and player control buttons are still clickable but have no effect.
Add a new signal named playerListEmptied(). When the proxy list is empty,
the signal is emitted and m_multiplexer is scheduled to be deleted, so
the media player applet on the desktop can indicate the right status of
no player opened.
BUG: 446098
Dependency
!1219 (merged) must be merged first.
Effect
| After plasmashell starts | Open Audacious | Close Audacious | |
|---|---|---|---|
| After this MR |  |
 |
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| Before this MR |  |
 |
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