giosrc: Add support for growing source files

Add a way for applications to specify that the underlying file is
growing which implies that the source won't EOS when reaching the end
of the file but instead start monitoring it and start reading it again
whenever a change is detected.

Also add a validate test to check the behavior
34 jobs for !937 with giosrc_growing_file in 26 seconds (queued for 3 seconds)
detached
Status Job ID Name Coverage
  Build Docker
passed #5802528
alpine amd64 manifest builder docker

00:00:16

passed #5802527
android docker

00:00:13

passed #5802526
cerbero fedora amd64 docker

00:00:16

passed #5802525
fedora amd64 docker

00:00:17

passed #5802529
gst-indent amd64 docker

00:00:13

 
  Preparation
passed #5802531
gst indent

00:00:09

manual #5802530
manual
manifest
 
  Build
created #5802540
gstreamer
build cerbero cross-android universal
created #5802544
gst-ios-13.2
build cerbero cross-ios universal
created #5802541
gstreamer
build cerbero cross win32
created #5802542
gstreamer
build cerbero cross win64
created #5802539
gstreamer
build cerbero fedora x86_64
created #5802543
gst-macos-10.15
build cerbero macos x86_64
created #5802545
1809 gstreamer-windows windows docker
build cerbero msvc x86_64
created #5802535
build clang fedora x86_64
created #5802538
1809 windows docker allowed to fail manual
build msys2
created #5802532
build nodebug fedora x86_64
created #5802533
build static fedora x86_64
created #5802534
build static nodebug fedora x86_64
created #5802536
1809 windows docker
build vs2017 amd64
created #5802537
1809 windows docker
build vs2017 x86
 
  Test
created #5802546
gstreamer
check fedora
created #5802547
gstreamer
integration testsuites fedora 1/4
created #5802548
gstreamer
integration testsuites fedora 2/4
created #5802549
gstreamer
integration testsuites fedora 3/4
created #5802550
gstreamer
integration testsuites fedora 4/4
created #5802554
gstreamer
valgrind bad
created #5802551
gstreamer
valgrind base
created #5802555
gstreamer
valgrind ges
created #5802552
gstreamer
valgrind good
created #5802553
gstreamer
valgrind ugly
 
  Integrate
created #5802556
cross-android universal examples
created #5802558
gst-ios-13.2
cross-ios universal examples
created #5802557
documentation