dbus: remove silly configuration option regarding unique name

Register both names unique and not. Fail if the unique name cannot be
obtained.
(cherry picked from commit daf9bb252d940d3194d74620a127a8d0df7c81d2)
dbus: do not spam at startup
(cherry picked from commit 63b3ed339d118757ec7dd112a78845046c00569b)
dbus: really remove the configuration option

(The previous commit only made it inoperant)
(cherry picked from commit d9f36235b8671491e6ec14c0ce4bbce337bcdc06)
dbus: remove excessive main loop debugging
(cherry picked from commit 485d2aa510d1067af31c479964e7235da146ac4f)
dbus: remove useless callback and fix warnings
(cherry picked from commit 6707159eedaf6cd9b2a62df0b48cbe9acecf9d37)
dbus: Fix the instance identifier part of the MPRIS bus name

The D-Bus specification forbids parts of well-known bus names to begin
with a digit. This patch changes the instance-specific part of the bus
name to .instance<pid> instead of -<pid> in order to comply with the
MPRIS v2.2

see: http://specifications.freedesktop.org/mpris-spec/2.2/#Bus-Name-Policy
(cherry picked from commit 77f036c81b3da31d156360fb6ca56f9bab1df11e)
dbus: Update comments related to the bus name policy
(cherry picked from commit e072818352c8b62d3f65726a5060999194806b28)
dbus: Return an int64 in the Position property getter

According to the MPRIS specification, the Position property of the
Player object must be an int64.

dbus microsecond position overflows the unsigned 32-bit integer at
about 35:48 into a track's playback.  A 64-bit integer still means
an overflow, but after more than 292000 years into a track's playback.

Signed-off-by: Mirsal Ennaime <mirsal@videolan.org>
(cherry picked from commit 7531cecfd40941a7d21b4566cc3b0ee964290090)
dbus: Fix the Seek method's introspection data

The position is an input parameter, not a return value.

Signed-off-by: Mirsal Ennaime <mirsal@videolan.org>
(cherry picked from commit d77c14f084c50ec3d5bd20fc09f0057e397d01ca)
dbus: Fix the CanSeek property getter

Close the D-Bus message when sending the value of the CanSeek property
in the Player object.

Signed-off-by: Mirsal Ennaime <mirsal@videolan.org>
(cherry picked from commit bc2987f3e14694a90bae1c8b3aaede8519a950a3)
dbus: Use the AfterTrack parameter in the tracklist's Add method
(cherry picked from commit b64a3e09ece630d1843058df48b3aa3f8c00ebbc)
single instance: Avoid initializing twice because of dbus activation

The single instance mode currently tries to contact another VLC instance
through dbus in order to find out if one is running. With dbus activation,
it results to the dbus daemon launching a new VLC instance while the
first one blocks until the new one answers the call

This patch uses org.freedesktop.DBus.NameHasOwner instead in order to get
an answer from the dbus daemon without it launching a second instance.
(cherry picked from commit bcc158b70019bdd2d1ab647173cb1ea41751f706)
single instance: append tracks as specified in MPRIS 2.2

Use /org/mpris/MediaPlayer2/TrackList/Append instead of / as the
AfterTrack argument to org.mpris.MediaPlayer2.AddTrack for appending
(cherry picked from commit 0376739feee15fa4636e30e7c85f1be97f2d74f9)
dbus: Fix seek detection

Closes: #6802
(cherry picked from commit 1b2ae82caddba30d5ea32317997d4464957e582c)