DoF strength varies according to render resolution #5874

The size of the DoF effect is fixed in pixel. As a result, the blurring strength is strongly dependent on render resolution, meaning that changing the base resolution or the render resolution factor will change DoF strength.

For example, blurring will be much weaker when the game is rendered at 2160p than at 720p, DoF blurring will be much stronger when picking 50% render resolution factor instead of 100%.

Instead, the blur strength should be made independent from the render resolution.

This relates also to the glow issue reported here: #5587