A deform-only modifier that needs access to normals need a copy of
evaluated mesh with those normals updated, when it is not the first one
in the stack.
That issue had been partially fixed in Object mode a long time ago
(see T23673), but it was still broken for deform-only stacks cases.
And it was also completely missing from the Edit mode code
(`editbmesh_calc_modifiers()` function).
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