Allow use of non-fullscreen resolutions in borderless window mode

[vrad-exe]

In P2CE, the resolution and aspect ratio dropdowns get forced to your native screen resolution and grayed out when "Fullscreen Windowed" (borderless window) mode is selected. This is the convention in most modern games that have a borderless window setting and I personally find it to be quite annoying and pointlessly restrictive. Vanilla Portal 2 does allow non-fullscreen borderless window mode, so P2CE should too.

P2CE:

Portal 2:

[pivotman319-owo]

would probably need to be done on the c++ backend

[vrad-exe]

I don't think so, I didn't mention it but this does work when setting the resolution from the command line or with mat_setvideomode, it's just the UI that has these disabled

[vrad-exe]

Oh nvm it seems like this is done from C++.....for some reason