playbin3: Propagate sink context

When the playsink's sink is activated its state is set to READY but it remains
unlinked. So, in order for decodebin3 to potentially reuse the context later on,
the whole playbin3 needs to have it internally stored.
25 jobs for playbin3-context in 58 minutes and 5 seconds (queued for 4 seconds)
latest
Status Job ID Name Coverage
  Preparation
passed #512071
gst indent

00:00:35

passed #512070
manifest

00:00:24

 
  Build
passed #512080
build cerbero android universal

00:10:44

passed #512081
build cerbero cross win32

00:17:13

passed #512082
build cerbero cross win64

00:07:11

passed #512079
build cerbero fedora x86_64

00:15:39

manual #512084
gst-ios-12.2 allowed to fail manual
build cerbero ios universal
passed #512083
gst-macos-10.14
build cerbero macos x86_64

00:08:35

passed #512072
build fedora x86_64

00:16:36

passed #512078
docker windows 1607
build msys2

00:11:45

passed #512073
build nodebug fedora x86_64

00:09:35

passed #512074
build static fedora x86_64

00:12:26

passed #512075
build static nodebug fedora x86_64

00:18:35

passed #512076
docker windows 1607
build vs2017 amd64

00:10:06

passed #512077
1607 windows docker
build vs2017 x86

00:10:06

 
  Test
passed #512448
check fedora

00:03:38

passed #512086
integration testsuites fedora

00:28:22

passed #512090
valgrind bad

00:06:53

passed #512087
valgrind base

00:17:21

passed #512091
valgrind ges

00:06:37

passed #512088
valgrind good

00:19:05

passed #512089
valgrind ugly

00:02:40

failed #512085
check fedora

00:03:25

 
  Integrate
passed #512092
android universal examples

00:06:52

passed #512093
documentation

00:05:17