glib: Fix named destinations
Named destinations may be described by bytestrings, containing embedded NULs and not being NUL terminated. That means they cannot be exposed directly as char*.
The alternatives are to escape the string from the internal representation when exposing it in the API (e.g. in PopplerDest.named_dest), or to add parallel API exposing it as GString, or GBytes. This patch chooses the first option, since the presence of these named destionations in the public, not sealed, PopplerDest struct means that the second option would need more API additions. The chosen option is simpler, and does not need the API users to adapt unless they create the named dest strings themselves, or consume them in ways other than calling poppler APIs.
The escaping scheme chosen simply replaces embedded NUL with "\0" and escapes a literal backslash with "\". This is a minimal ABI change in that some strings that previously worked unchanged as destinations (those containing backslash) now don't work, but on the other hand, previously it was impossible to use any destinations containing embedded NULs.
Add poppler_named_dest_{from,to}_bytestring() to perform that conversion, and clarify the documentation for when you need them.
Based on a patch by José Aliste jaliste@src.gnome.org.