Add VideoStreamPlayer UpdateMode to not process the invisible

[smix8]

Adds UpdateMode to VideoStreamPlayer for better performance and control in gui heavy setups with lots of small video streams.

Performance

These performance spikes seen here are with 10+ smaller video stream players active that are all from different gui elements off-screen and not visible on a 144 hz monitor with uncapped frame rate. Part of the big jump is also caused by running into a physics death spiral due to all the senseless processing for invisible videos going on behind the scene.

The changes in this PR with visibility check is what causes the performance to reset to manageable levels because it stops processing all the videos that are in hidden menus or off-screen automatically (in this example case when the graph is at its lowest just 1 or zero videos are processing because those can actually be seen). There are other performance issues with the VideoStreamPlayer node for other PRs to fix but this is a first step.

Update modes

• UPDATE_DISABLED
  Same as paused but without changing properties that would cause unwanted side effects in code.
• UPDATE_WHEN_VISIBLE
  The recommended winner mode that only processes what can actually be seen on screen. Works by using the node visibility and the CanvasItem visibility notifier.
• UPDATE_ALWAYS
  The current default that updates and processes everything all the time no matter what.

While UPDATE_ALWAYS would match with the current way the VideoStreamPlayer is behaving I recommend using the UPDATE_WHEN_VISIBLE as the new default.

It commonly does not make that much sense to process videos while not at all visible. That situation frequently is found in Control based gui menus where users park menus with video backdrops for later use. Since the video player has no dedicated debugger all users see is an increased process() time not understanding what is causing it.

I encountered these performance issues many times over in Godot projects where users would never free their menu backdrop movies because it would cause stutters when loading the (quick) menu at runtime so they entire gameplay time they would just process in the background movies that no one sees wasting performance. Sure they could add scripts to pause and un-set the Stream but they are commonly not doing that and it would be better to do it automatically.

[KoBeWi]

Did you try VisibleOnScreenEnabler2D? Put one as child of VideoStreamPlayer and it should have the same effect.

[smix8]

Did you try VisibleOnScreenEnabler2D? Put one as child of VideoStreamPlayer and it should have the same effect.

Working with extra nodes is not a viable solution because it causes node and tree related issues, especially when running tool scripts for custom video players. The node-forced video playback is flawed in many ways but that is mostly addressed by fixing the script exposed playback functions with #114515. This PR here is mostly to protect the inexperienced Godot user from running into performance issues by having a more sensible default behavior.