We used to use two methods to save a document: poppler_document_save
and poppler_document_save_a_copy. The latter only saves a copy of
the original document, discarding any change done (e.g. forms and
annotations). However, after a document has been modified and saved,
if there is no new change and the user saves the document, it will
discard even the previous saved changes to preserve a copy of the
original document.

By only using poppler_document_save to save the content of the
current document opened in Atril, to avoid data loss made between
saves.

https://bugzilla.gnome.org/show_bug.cgi?id=770012

Adapted from the original commit at:
https://gitlab.gnome.org/GNOME/evince/-/commit/26dc2f52

Co-authored-by: Eric Park <me@ericswpark.com>

Based on an XReader change[1], look up the MathJax source at configure
time for better portability.  If not specified manually, look in the
common locations.

This adds the --with-mathjax-directory=DIR configure option to manually
specify the location, overriding the automatic discovery.

The Meson part already exists, although was not used by the code.

[1]: https://github.com/linuxmint/xreader/commit/9c6f363ad47f33b290d270489e50f7ad6071987a

Import test source from XReader[1].  This is not as useful as it might
seem as it's not a unit test, but it's still nice to have an easy way
to manually test this code, and reduces differences with XReader,
especially in the Meson build system.

[1] https://github.com/linuxmint/xreader/blob/master/backend/comics/test-ev-archive.c

This allows enabling the backend automatically depending on whether the
dependencies are satisfied or not, like Autotool's counterpart.

By default, the PDF backend is force-enabled and the Pixbuf backend is
disabled, as with Autotools.

Signed-off-by: Oz Tiram <oz.tiram@gmail.com>

Signed-off-by: Oz Tiram <oz.tiram@gmail.com>

Signed-off-by: Oz Tiram <oz.tiram@gmail.com>

Mostly copy and paste from linuxmint/xreader

Signed-off-by: Oz Tiram <oz.tiram@gmail.com>