object: Use g_object_notify_by_pspec()

`g_object_notify()` actually takes a global lock to look up the
`GParamSpec` that corresponds to the given property name. It's not a
huge performance hit, but it's easily avoidable by using the
`_by_pspec()` variant.
26 jobs for wip/nielsdg/notify-by-pspec in 137 minutes and 48 seconds (queued for 2 seconds)
Status Job ID Name Coverage
  Preparation
passed #532890
gst indent

00:00:33

passed #532889
manifest

00:00:23

 
  Build
passed #532899
build cerbero android universal

01:01:27

passed #532900
build cerbero cross win32

00:55:33

passed #532901
build cerbero cross win64

00:59:29

passed #532898
build cerbero fedora x86_64

00:30:13

manual #532903
gst-ios-12.2 allowed to fail manual
build cerbero ios universal
passed #532902
gst-macos-10.14
build cerbero macos x86_64

00:54:44

passed #532891
build fedora x86_64

00:07:20

passed #532897
docker windows 1607
build msys2

00:13:47

passed #532892
build nodebug fedora x86_64

00:04:35

passed #532893
build static fedora x86_64

00:12:54

passed #532894
build static nodebug fedora x86_64

00:12:06

passed #532895
docker windows 1607
build vs2017 amd64

00:10:58

passed #532896
docker windows 1607
build vs2017 x86

00:12:41

 
  Test
passed #532904
check fedora

00:06:41

passed #533562
integration testsuites fedora

00:14:12

passed #532910
valgrind bad

00:12:51

passed #532907
valgrind base

00:25:03

passed #532906
valgrind core

00:50:06

passed #532911
valgrind ges

00:10:05

passed #532908
valgrind good

00:12:11

passed #532909
valgrind ugly

00:02:14

failed #532905
integration testsuites fedora

00:54:53

 
  Integrate
passed #532912
android universal examples

00:10:43

passed #532913
documentation

00:04:01