Allow characters outside of BMP in the "filter by string" box

[Lorp]

Currently, characters outside of the BMP are not handled via the "filter by string" box, since only cmap Format 4 is handled, so only unicode ids <65536. Therefore characters such as U+1F60A ("😊") cannot be selected via that string.

Integration of samsa-core v2 will fix this, since it handles cmap Format 12.