Async parse methods should return Task

[mfkl]

Would be good to return a Task from Media.ParseAsync and Media.ParseWithOptions (also async).

Notes:

• ParseAsync is deprecated. Should favor using ParseWithOptions.
• ParseWithOptions is actually async (Should add Async in C# method name?).
• Returning a Task can be implemented by listening to the libvlc_MediaParsedChanged event.
• ParseWithOptions timeout: "maximum time allowed to preparse the media. If -1, the default "preparse-timeout" option will be used as a timeout. If 0, it will wait indefinitely. If > 0, the timeout will be used (in milliseconds)."
• Cancellation token should call ParseStop.

libvlc C API doc
https://www.videolan.org/developers/vlc/doc/doxygen/html/group__libvlc__media.html#ga55f5a33e22aa32e17a9bb75decd1497b
https://www.videolan.org/developers/vlc/doc/doxygen/html/group__libvlc__media.html#gae7cedd70494f7110df5ce8e704ffb9d4
https://www.videolan.org/developers/vlc/doc/doxygen/html/group__libvlc__media.html#gaa6ee5287c7b4620cc86b89518173a7dc