glib: implement rotation for 'flagNoRotate' annots

previously poppler_page_get_annot_mapping() function
was ignoring to rotate annots flagged as 'flagNoRotate'
probably because they require a special rotation where
the annotation pivots on the upper left corner, as
described in PDF 1.7 spec "8.4.2 Annotation Flags"
NoRotate flag.

Added support for that, while refactoring the code to
make it more readable.

Fixes #767
6 jobs for BUG_implement_flagNoRotate in 3 minutes and 58 seconds (queued for 1 second)
latest
Status Job ID Name Coverage
  Build
passed #1780199
build

00:03:49

passed #1780204
build_android

00:02:04

passed #1780200
build_clang_libcpp

00:03:57

passed #1780203
build_clazy

00:02:21

passed #1780202
build_mingw64_fedora

00:02:45

passed #1780201
build_ubuntu_16_04

00:01:47