Camera: Add eyes-free videography metadata

- Add EFV metadata and include them as extension keys
- ExtensionCaptureRequest, ExtensionCaptureResult are new classes for extension-specific keys. These keys will be marked as hidden in the corresponding CameraMetadata classes and exposed to the public API via the Extension key classes.
- EFV (and future extension specific keys) will be annotated as @ExtensionKey to differentiate them from hidden keys and exempt them from restrictions imposed on hidden keys (such as allowing exposure of keys through CaptureRequest.getKeys())

Test: Camera CTS test
Bug: 300065685
Change-Id: I844eeed51b9abc97b3142d92fb03fb52e97e0a01