Improve window presentation at native resolution

[Filoppi]

This PR fixes some edge cases introduced by: https://github.com/dolphin-emu/dolphin/pull/11889 https://github.com/dolphin-emu/dolphin/pull/12000 where if the game already outputted to a near perfect ~4:3 resolution, dolphin would pick a window draw resolution that was "off" by one pixel, which would make it unnecessarily blurry. This was technically right, but is not really desired, so we put a one pixel threshold given that this case is relatively common in GC games played at native resolution. These screenshots show the difference of how it acted before and after the PRs above: with this PR it now looks identical to the crisp older version again.

A full explanation of the fix is here: