Register file associations when installing mpv.net

[soredake]

Is your feature request related to a problem? Please describe.
Right now, installer are not doing this.

Describe the solution you'd like
Registering file associations when install mpv.net.

Describe alternatives you've considered
Using built-in menu to do this in mpv.net

Additional context
Example innosetup installer that registers file associations https://github.com/nomacs/nomacs/blob/539959ec46e1ecb594aded0d0a7f58412f05b51e/installer/nomacs-setup.iss