Ensure proper camera projection/scale and resolution/AR handling

[inodentry]

In order to have the game look good at any resolution or aspect ratio (incl ultrawide), we need to come up with a strategy that balances looks and gameplay.

It is important to:

• ensure integer scale (number of screen pixels to logical pixel), so pixel art looks good
• ensure the player does not see things they are not supposed to see
• ensure things they are supposed to see do not get cut off
• show roughly the same content to all users
• be able to design levels without too much worry about what's going to be visible on screen

Therefore, here is the current best proposal for how to implement this:

• Pick the scaling factor so that there are roughly 180 vertical pixels on the screen, at the current resolution
• Have a min/max X/Y for the camera, so we can limit the viewable area
• Support some additional panning so that the user can move the camera a little
• Have a limit to the horizontal AR
• Have a vignette effect to fade to black around the edges. Avoid hard black bars for ultrawide users.