meson: List libraries and their corresponding gir definition

Introduces a `libraries` variable that contains all libraries in a
dict with the following format:

``` meson
'lib': library_object
'gir': {full gir definition in a dict }
```

It therefore refactors the way we build the gir so that we can reuse the
same information to build them against 'gstreamer-full' in gst-build
when linking statically
23 jobs for !140 with static_gir in 9 seconds (queued for 2 seconds)
latest detached
Status Job ID Name Coverage
  Preparation
passed #3326821
gst indent

00:00:09

manual #3326820
manual
manifest
 
  Build
created #3326837
gstreamer
build cerbero cross-android universal
created #3326841
gst-ios-13.2
build cerbero cross-ios universal
created #3326838
gstreamer
build cerbero cross win32
created #3326839
gstreamer
build cerbero cross win64
created #3326836
gstreamer
build cerbero fedora x86_64
created #3326840
gst-macos-10.15
build cerbero macos x86_64
created #3326828
build clang fedora x86_64
created #3326835
1809 windows docker allowed to fail manual
build msys2
created #3326823
build nodebug fedora x86_64
created #3326825
build static fedora x86_64
created #3326827
build static nodebug fedora x86_64
created #3326830
1809 windows docker
build vs2017 amd64
created #3326833
1809 windows docker
build vs2017 x86
 
  Test
created #3326842
gstreamer
check fedora
created #3326843
gstreamer
integration testsuites fedora 1/4
created #3326844
gstreamer
integration testsuites fedora 2/4
created #3326845
gstreamer
integration testsuites fedora 3/4
created #3326846
gstreamer
integration testsuites fedora 4/4
 
  Integrate
created #3326847
cross-android universal examples
created #3326849
gst-ios-13.2
cross-ios universal examples
created #3326848
documentation