Blender Git Loki

UV: tweak face select behavior

When the mouse cursor is inside the UV face,
extend the selection threshold.

This means when zoomed in, a face can always be selected when the cursor
is inside it.
In the case of multiple overlapping faces - the face with the closest
center is used.

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Prior to 246efd7286f6187e4dd4b3edcc79cccb1746bb1d, the UV selection
threshold was scaled by the zoom level, so selecting a face when zoomed
in close would often often select faces even when the on-screen center
was outside the intended threshold.

Having a zoom-independent threshold may require more precision than
users are used to.

This change addresses this.