Core/WiimoteReal: Wii remote connection pool and source change cleanup.

[jordan-woyak]

Replaced wide usages of g_wiimote_sources with get/set functions.
Made the unnamed enum type an enum class, WiimoteSource.

Connected real Wii remotes are now added to a "pool" when no open slot is available.
Wii remotes in the pool have LEDs 1 and 4 lit to make it apparent they are not active.
They are disconnected per normal after 5 seconds.
This allows reassigning sources and reordering remotes without the hassle of Bluetooth re-connections.

This is mainly in preparation for Wii remotes in controller interface.
My plan is an option on the Wii remote dialog, "Connect Wii Remotes for input configuration" (or something with a better name).
Enabling it will first fill any "Real" slots but additional remotes will be sent to controller interface.
Disabling the option will send spurious remotes to the pool.

I think this "pool" will make things less horrible for users that are playing around with options.
Making Wii remote connections can be not-fun, especially on Windows/macOS.
Holding on to a connection for a few seconds when between configurations will give users a better experience

Perhaps someone ambitious might make a UI for the pool.
Remotes could be identified with rumble and sent to a slot or controller interface.

This all of course only affects emulated Bluetooth.

[leoetlino]

(This is really only a very partial review)

[iwubcode]

I haven't tested this but code wise, this looks really nice!