Create new toPopplerAdditionalActionType private function

This adds API to access AnnotWidget actions which
are associated with a FormField.

Yes what we're doing there is a bit nasty but it works :D

Parent already has a proper constructor that initializes stuff and on top of that the sizeof was of the pointer and not of the class itself

As shown by Adam in f559cc94 it was a
noop since we were not filling the hash it tried to get info from

Make UnicodeMap a move-only type to simplify the initialization of residentUnicodeMaps s.t. it is closer to the GooHash-based version.

It wasn't working since the if mentioned LIBOPENJPEG2_INCLUDE_DIR instead of LIBOPENJPEG2_INCLUDE_DIRS
and when fixing the typo it broke the build because we were not defining USE_OPENJPEG2, so better just
remove the broken if code

Bug #105194

Bug #105558

Bugs #104942, #103238

Going to the position -1 of an array is undefined behaviour, so don't do
it

Bug #105970

Bug #106244

It was doing that anyway but in a more complex way.

Added a note into the docu so that people can volunteer to come
and fix it if someone is using it

The key is uppercase B with lowercase L. Not I.

Bug #104881

After the discussion on the mailing list, also using unique_ptr was
wrong

In GfxGouraudTriangleShading::parse

Bug #106061

Didn't manage to make fontconfig build, still nice to have poppler
available.

We find it explicitly because it may be elsewhere.