* Fixed issue #1609 (Cell.read doesn't read LayoutMetaInfo)
This also includes some more functions:
- Layout#merge_meta_info, Layout#copy_meta_info
- Layout#clear_all_meta_info
- Cell#merge_meta_info, Cell#copy_meta_info
In addition, meta info is merged when importing a layout from
another file (Layout/Import -> Other Layouts into current).
* Meta info support in layout diff (for testing), implemented meta info merge for GDS and OASIS readers with special conflict resolution modes
* Undo support for meta info - this way we do not loose meta info when we delete a cell and undo
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Co-authored-by: Matthias Koefferlein <matthias@klayout.de>
Matthias Köfferlein