Based on #62896, only implements the BPM support part.
* Implements BPM support in the AudioStreamOGG/MP3 importers.
* Can select BPM/Bar Size and total beats in a song file, as well as edit looping points.
* Looping is now BPM aware
* Added a special importer UI for configuring this.
* Added a special preview showing the audio waveform as well as the playback position in the resource picker.
* Renamed `AudioStream::instance` to `instantiate` for correctness.
MultiplayerSynchronizers can now be configured to limit their visibility
to a subset of the connected peers, if the synchronized node was spawned
by a MultiplayerSpawner (either automatically or via custom spawn) the
given node will also be despawned remotely.
The replication system doesn't have the logic to handle subspawn
directly, but it is possible to handle them appropriately by manually
updating the visibility of the parent before changing the one of the
nested spawns via the "update_visibility" function.
The visibility of each MultiplayerSynchronizer can be controlled by
adding or remove filters via "[add|remove]_visibility_filter(callable)".
To further optimize the network code, visibility filters can be configured
to be automatically updated during idle or physics frame, or set to always
require manual update (via the "update_visibility" function).
`rendering/quality/shadows` is now `rendering/quality/positional_shadow`
to explicitly denote that the settings only affect positional light shadows,
not directional light shadows.
Shadow atlas settings now contain the word "atlas" for easier searching.
Soft shadow quality settings were renamed to contain the word "filter".
This makes the settings appear when searching for "filter" in the
project settings dialog, like in Godot 3.x.
And finally remove the 'frames' property which was added for compatibility with 2.1
in bed3efb17e.
Fixes#21765.
The 'animations' property on the other hand is needed, contrarily to what its comment
said (copy-paste mistake probably).
Also removes unused '_get_animation_list'.
This ensures videos are always visible as soon as a video file
is specified in the VideoStreamPlayer node. The node will no longer
be resized to 0×0 by default, making the video invisible in the process
(even if the audio can still be heard).
