allow to toggle off cf's textarea and input sizes if $Cols/$Rows are set to undef

we have default $Cols/$Rows in /Element/EditCustomFields, so it doesn't help
much in core for now, but this gives customers the flexibility to toggle off
the size/cols/rows html attributes for some custom fields, e.g.

    <& /Elements/EditCustomField, ..., Cols => undef &>
Merge branch '4.0/toggle-off-cf-input-size' into 4.0-trunk