LineStyles are not copied when elements referencing them are copied between iModels

[ColinKerr]

This issue was raised via discussion question: #7642

From that discussion @bbastings says:

I see that DgnImportContext currently has the code to try to copy the line style information over commented out?

DgnStyleId DgnImportContext::_RemapLineStyleId(DgnStyleId sourceId)
{
if (!IsBetweenDbs())
return sourceId;

DgnStyleId dest = FindLineStyleId(sourceId);
if (dest.IsValid())
return dest;
#if defined(NEEDSWORK_LINESTYLES) // importers are not tested so don't risk passing along bad data.
dest = LineStyleElement::ImportLineStyle(sourceId, *this);
AddLineStyleId(sourceId, dest);
#endif

return dest;
}