Add a camera feed demo in misc

[shiena]

This is a demo project for camera feed and camera server.

Supported Platforms

• Linux
• Android (4.5 or later)

Limitations

Pull requests have been proposed for Windows, iOS and Web.

• Add CameraFeed support for Windows godot#105476
• Add CameraFeed support for Windows godot#108538
• Add CameraFeed support for iOS godot#106305
• Add CameraFeed support for Web godot#106784

macOS and iOS are incomplete due to bugs.

• Support CameraFeed format on macOS godot#106777
• [macOS] Fix missing frame_changed signal to CameraFeed godot#104809

Support CameraServer.feeds_updated signal.

• Add CameraServer feeds_updated signal, and document async behavior godot#108165

Preview

[Calinou]

Note that the demo requires 4.5 (even on unsupported platforms), as it references the monitoring_feeds property which doesn't exist on 4.4.1. This is not essential to fix to merge (it's fine for this demo to be 4.5+), but I thought I'd mention nonetheless.

Some feedback:

• The demo should be switched to the Compatibility rendering method if it doesn't use features exclusive to Forward+/Mobile.
• The demo's folder should be renamed from camerafeed to camera_feed.
• application/run/low_processor_mode should be enabled in the Project Settings to reduce CPU/GPU utilization when idle.

[shiena]

@Calinou
Updated based on review feedback:

• Add require 4.5
• Switch to the Compatibility rendering
• Rename from camerafeed to camera_feed
• Enable application/run/low_processor_mode

[Calinou]

The demo should use a lower window size on desktop platforms. Otherwise, on a 1080p display, it'll look like this when run from the editor with game window embedding enabled:

You can do this by changing Window Width Override and Window Height Override to 480 and 854 respectively. This will allow it to fit on a 1080p display. (The setting is ignored on mobile platforms.)

[shiena]

• Changed Window Width Override and Window Height Override