Separate WindowsRuntimeComponent into its own source code and code generators

[angularsen]

See #576 (comment).

Basically WRC has been a major friction for maintainers and contributors of the library for a long time.
We don't seem to have a lot of consumers of the WRC target so the pain outweighs the gain and the WRC target as a means of sharing .NET libraries with JavaScript and C++ UWP apps don't seem to have a lot of interest in general.

Adding new units and quantities is still a breeze in WRC, so what we need to do is split out the code generator scripts for WRC and get its full copy of all the shared source code, then we can still add new units to both UnitsNet and WRC and produce new versions as before - it just won't get things like Quantity and QuantityInfo in the future.

[angularsen]

Waiting for some input from the person who originally asked for WRC support, maybe he knows something about WRC that we don't.

Me and @tmilnthorp are pretty much agreed on doing this unless there are very convincing arguments to keep it alive.

[angularsen]

After some input from the person who originally asked for WRC support, I am currently leaning towards removing WRC support and instead add it back (with its own source code and code generators as described above) if someone actually comes asking for it to be updated.

I suspect very few, probably none, will care that no new nugets are released for WRC.

See: #576 (comment)