Problem was that with forward-referenced text strings
in OASIS, StringRef objects were created (string placeholders).
Those where not properly migrated when transferring the foreign
layouts into DEF space, causing a memory corruption issue.
This solution is to provide a central, singleton string
repository. This needs to be MT safe (reference counting)
which should also fix potential problems when accessing
StringRef-based Text objects from multiple threads.
Fixed some more glitches while doing so:
* cell.name (gsi) was giving "basic_name", now it's changed to the
internal name to be consistent with "name=". The "functional name"
is still available as "basic_name".
* The basic name was rendering "<defunct>..." for defunct cells
and has been changed to the functional name. Otherwise this
is not accessible.
Basic change: DeepShapeStore+CellMapping uses (new) hier_generation_id of Layout to figure out
if the hierarchy has changed and the cache needs update.