No functional changes.

Regression from ad183c8f

It would have been used as NULL otherwise

and better handling of leaks

It need to be ported to the new player, playlist and tree.

The vout is now always present, there is no need to use the old playlist as a
proxy.

IMPORTANT: the video filter settings will now only change for the main vout. We
need to define a way to change vout settings for other windows.

The aout is always present, there is no need to use the old playlist as a
proxy.

Since the vout is now persistent, there is no need to store the variables on an
intermediate vlc_object_t (that was wrongly set to the interface during the
last UI merge).

IMPORTANT: the video filter settings will now only change for the main vout. We
need to define a way to change vout settings for other windows.

No real functional changes. Changes the callback and enum names to reflect the
real event: vout are now started and stopped. The same vout can be started and
stopped several time.

It must be replaced with legacy vout variables handling.

It must be replaced with legacy vout variables handling.

Vout recycling as keeping the same "vout display" plugin and not
disabling/enabling the window.

Add input_resource_StopFreeVout: Used to stop the re-used vout if there is no
video following the current input.

The vout is now always closed or paused from input_resource_PutVout(). Only the
main vout is paused, all additional vouts will be closed. The main vout will be
actually closed from input_resource_StopFreeVout(), when we are sure that the
next input doesn't have video.

It was only called from ES_OUT_SET_*_BY_ID controls. The new player is calling
ES_OUT_SET_* directly that was not called TerminateVout.

vout_Pause will clean variables that are used by the current owner (clock,
mouse) and put the vout to sleep. On a Next vout_Request, if the vout is
re-used, vout_Resume will store new owner variables and resume the thread.

The first vout created (the main one) will now always be the first vout of the
array. It's important to keep the same reference on the first vout, since its
window plugin is likely linked to an interface. This commit ensure that this
first vout will always be the first vout used by the first video decoder or
visualiser.

And add its locked version: into input_resource_PutVoutLocked.