find, glib: Enhance find to support multi-line matching

On the backend side, add adding 5 new parameters to TextPage::findText(),
4 to return coords for the part of the match that falls on the next line,
and 1 to specify whether hyphen was ignored at end of the first line.

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 binding, 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 qt5 binding still allows for the creation of
tests for this feature (using the qt5 test framework) which
this commit *do includes*. But a more complete binding (with
a new return type that includes 'next_line' and 'after_hyphen'
boolean fields) is left to do for qt5 binding 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
6 jobs for BUG_search_across_lines in 10 minutes and 15 seconds (queued for 14 seconds)
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passed #678764
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passed #678769
build_android

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passed #678765
build_clang_libcpp

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build_clazy

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build_mingw64_fedora

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build_ubuntu_16_04

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