meson: List libraries and their corresponding git definition

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

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

It therefore refactors the way we build the git so that we can reuse the
same information to build them against 'gstreamer-full' in gst-build
when linking statically
35 jobs for static_gir in 3 minutes and 27 seconds (queued for 16 seconds)
latest
Status Job ID Name Coverage
  Build Docker
passed #4691476
alpine amd64 manifest builder docker

00:00:19

passed #4691474
android docker

00:01:10

passed #4691472
cerbero fedora amd64 docker

00:02:57

passed #4691471
fedora amd64 docker

00:03:14

passed #4691478
gst-indent amd64 docker

00:00:10

 
  Preparation
passed #4691482
gst indent

00:00:12

manual #4691480
manual
manifest
 
  Build
created #4691495
gstreamer
build cerbero cross-android universal
created #4691502
gst-ios-13.2
build cerbero cross-ios universal
created #4691496
gstreamer
build cerbero cross win32
created #4691497
gstreamer
build cerbero cross win64
created #4691494
gstreamer
build cerbero fedora x86_64
created #4691499
gst-macos-10.15
build cerbero macos x86_64
created #4691504
1809 gstreamer-windows windows docker
build cerbero msvc x86_64
created #4691489
build clang fedora x86_64
created #4691493
1809 windows docker allowed to fail manual
build msys2
created #4691484
build nodebug fedora x86_64
created #4691486
build static fedora x86_64
created #4691487
build static nodebug fedora x86_64
created #4691490
1809 windows docker
build vs2017 amd64
created #4691492
1809 windows docker
build vs2017 x86
 
  Test
created #4691508
gstreamer
check fedora
created #4691510
gstreamer
integration testsuites fedora 1/4
created #4691512
gstreamer
integration testsuites fedora 2/4
created #4691515
gstreamer
integration testsuites fedora 3/4
created #4691517
gstreamer
integration testsuites fedora 4/4
created #4691529
gstreamer
valgrind bad
created #4691521
gstreamer
valgrind base
created #4691519
gstreamer
valgrind core
created #4691533
gstreamer
valgrind ges
created #4691524
gstreamer
valgrind good
created #4691526
gstreamer
valgrind ugly
 
  Integrate
created #4691535
cross-android universal examples
created #4691539
gst-ios-13.2
cross-ios universal examples
created #4691537
documentation