This removes the reliance on Viewport shrinking, which fixes various
bugs with mouse input handling in 3D gizmos or the GridMap editor.
This also makes Half Resolution make use of the current 3D scaling
mode defined in the project setting (bilinear, FSR1 or FSR2).
When Half Resolution is checked, the Scaling 3D Scale value in the
project settings is halved in the editor. To ensure the 3D view
remaisn somewhat readable, the final value can't go below
the minimum value allowed in the project settings, which is 0.25.
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