On the backend side, adds 3 new parameters to TextPage::findText(),
one bool to enable the feature, one out PDFRectangle to store
the part of the match that falls on the next line, and one out
bool to inform whether hyphen was present and ignored at end of
the previous match part.

For the glib binding, this extends the public PopplerRectangle
struct by new members to hold additional information about
whether the rectangle belongs to a group of rectangles for the
same match, and whether a hyphen was ignored at the end of the
line. Since PopplerRectangle is public ABI, this is done by making
the public PopplerRectangle API return the enlarged struct, and
internally casting to the new struct when required, the new
members are accessible only via accessor functions.

For Qt5 Qt6 bindings, this commit only implements the new flag
Poppler::Page::AcrossLines (but no new function and no new
return data type) and if this flag is passed, the returned
list of rectangles will also include rectangles for the
second part of across-line matches.

This minimum Qt bindings still allows for the creation of
tests for this feature (using the Qt test framework) which
this commit *do includes*. But a more complete binding (with
a new return type that includes 'matchContinued' and 'ignoredHypen'
boolean fields) is left to do for qt backend maintainers
if they want to use this feature in eg. Okular.

So, as mentioned, this commit incorporates tests for the
implemented across-line matching feature, and the tests do
also check for two included aspects of this feature, which are:

 - Ignoring hyphen character while matching when 1) it's the
   last character of the line and 2) its corresponding matching
   character in the search term is not an hyphen too.

 - Any whitespace characters in the search term will be allowed
   to match on the logic position where the lines split (i.e. what
   would normally be the newline character in a text file, but
   PDF text does not include newline characters between lines).

Regarding the enhancement to findText() function which implements
matching across lines, just two more notes:

 - It won't match on text spanning more than two lines, i.e. it
   only matches text spanning from end of one line to start of
   next line.

 - It does not supports finding backwards, if findText() receives
   both <backward> and <matchAcrossLines> parameters as true, it
   will ignore the <matchAcrossLines> parameter. Implementing
   <matchAcrossLines> with backwards direction is possible, but
   it will make an already complex function like findText() to be
   even more complex, for little gain as eg. Evince does not even
   use the <backward> parameter of findText().

Fixes poppler issues #744 and #755
Related Evince issue https://gitlab.gnome.org/GNOME/evince/issues/333