DPI: add back option to control line width, tweak default width.

Adds thin/default/thick modes to add -1/0/1 to the auto detected line width,
while leaving the overall UI scale unchanged.

Also tweaks the default line width threshold, so thicker lines start from
slightly high UI scales.

Differential Revision: https://developer.blender.org/D2778

release/scripts/startup/bl_ui/space_userpref.py

@@ -218,6 +218,7 @@ class USERPREF_PT_interface(Panel):
         col = row.column()
         col.label(text="Display:")
         col.prop(view, "ui_scale", text="Scale")
+        col.prop(view, "ui_line_width", text="Line Width")
         col.prop(view, "show_tooltips")
         col.prop(view, "show_tooltips_python")
         col.prop(view, "show_object_info", text="Object Info")