This fixes missing selection updates in UV editor, both with GPU subdivision
and with the Modified Edges display option for modifiers in general.

It also fixes the UV editor incorrectly showing the cage mesh with deformed
coordinates. These are not yet supported by the UV selection system.

Changes:

• Always read selection state from the editmesh when building batches. The flags in the evaluated mesh can be outdated as selection bypasses depsgraph evaluation for performance, and instead may just clear the batches.
• runtime.is_original is only valid for the bmesh wrapper. The check for building the UV cage should only use that if the mesh is a bmesh wrapper.
• Don't create cage batches for objects whose mesh is in edit mode, but that are not themselves in edit mode, there is no need.