message: Add NEED_CONTEXT_ALL message type

GstElement can store multiple persistent context even if they are
all identical type. But GstBin will response the very first context
from NEED_CONTEXT message. This NEED_CONTEXT_ALL message will be used
for requesting all available specific contexts.
28 jobs for need-context-all in 51 minutes and 22 seconds (queued for 2 seconds)
latest
Status Job ID Name Coverage
  Preparation
passed #460580
gst indent

00:00:37

passed #460579
manifest

00:00:38

 
  Build
passed #460586
build cerbero android universal

00:10:07

passed #460587
build cerbero cross win32

00:10:23

passed #460588
build cerbero cross win64

00:08:55

passed #460585
build cerbero fedora x86_64

00:08:20

manual #460590
gst-ios-12.2 allowed to fail manual
build cerbero ios universal
passed #460589
gst-macos-10.14
build cerbero macos x86_64

00:06:49

passed #460581
build fedora x86_64

00:08:46

passed #460582
build nodebug fedora x86_64

00:06:33

passed #460583
build static fedora x86_64

00:12:53

passed #460584
build static nodebug fedora x86_64

00:11:38

 
  Test
passed #460666
check fedora

00:03:23

passed #460592
integration testsuites fedora

00:17:31

passed #460597
valgrind bad

00:12:42

passed #460594
valgrind base

00:15:43

passed #460593
valgrind core

00:16:45

passed #460598
valgrind ges

00:12:18

passed #460710
valgrind good

00:08:24

passed #460596
valgrind ugly

00:02:01

failed #460591
check fedora

00:06:16

failed #460686
valgrind good

00:21:36

failed #460672
valgrind good

00:13:27

failed #460671
valgrind good

00:14:49

failed #460665
valgrind good

00:12:41

failed #460595
valgrind good

00:13:12

 
  Integrate
passed #460599
android universal examples

00:08:27

passed #460600
documentation

00:04:28