multimedia/gstreamer1: Update to 1.24.8

Mk/Uses/gstreamer.mk:
- Sort, fix whitespace issues and typos
- Promote several common variables to improve maintainer QOL
*   There's now no need to set manually set PORTVERSION nor
    SOVERSION in several Makefiles
*   This will help to prevent not updating some components
*   A note has been added, however, to remind maintainers
    to remake distinfo for certain ports
- Improve documentation

multimedia/gstreamer1-plugins-webrtc:
- New port split from multimedia/gstreamer1-plugins-bad
- multimedia/gstreamer1-plugins-rust has been updated

Update gstreamer1 to upstream release 1.20.3

PR:		261585
Reviewed by:	riggs,jbeich,tcberner

Differential Revision:	https://reviews.freebsd.org/D36850

textproc/libxml2: bump all LIB_DEPENDS consumers

This is a separate commit to facilitate easier cherry-picking for
quarterly.

PR: 262853, 262940, 262877, 263126
Approved by: fluffy (mentor)

textproc/libxml2: bump all dependencies

This should make sure that all dependent ports will pick
up the new version commited with a13ec21cd733f67a9fc0dc00ab45268bdc236246

One more small cleanup, forgotten yesterday.
Reported by:	lwhsu

Remove # $FreeBSD$ from Makefiles.

Update GStreamer1 to 1.6.2.
Update GStreamer1-vaapi to 0.7.0.

* Spell GStreamer consistently. [1]
* Fix typo in py3kplist in py3-gstreamer1 [1]
* Improve plugins COMMENTS (more improvements welcome)
* Actually include the gstreamer1-libav update this time.

PR:		204204 [1] (based on)
Submitted by:	olivierd@ [1]

Update gstreamer1 ports to 1.6.0.

* gstreamer1-libav now uses ffmpeg from ports.
* New ports:
  * gstreamer1-validate: Tools to detect if elements are not behaving
    as expected, mainly aimed at developers, or advanced debugging.
  * gstreamer1-rtsp-server: Base foundation for building a rtsp
    server ontop of GStreamer
 * Bunch of new plugins like: mpg123, rsvg, libde265, openh264, x265 and dtls.

Release announcement:
 
http://lists.freedesktop.org/archives/gstreamer-announce/2015-September/000357.html

Obtained from:	gnome devel repo

Bump portrevision after png update

Update gstreamer 1.0 ports to version 1.2.4.

When linking a library libA with a library libB using libtool, if libB.la
exists, libtool will add all libraries libB.la refers to (dependency_libs
field) to the linker command line and store them in the dependency_libs
field of libA.la.  So everything that subsequently links with libA will also
link to these extra libraries.  This causes too much overlinking.

This commit modifies Mk/Uses/libtool.mk so it empties the dependency_libs
field in .la libraries during staging.  However, because .la libraries have
very limited use when dependency_libs is empty it makes sense to completely
remove them during staging.

So with this commit USES=libtool is modified to remove .la libraries and a
new form (USES=libtool:keepla) is introduced in case they need to be kept
(dependency_libs is still emptied).

Stagify Gstreamer ports.
Fix build of gstreamer and gstreamer1 with glib 2.38.x [1].
Update gstreamer and gstreamer-plugins to new rules, USES=gmake pathfix,
new LIB_DEPENDS syntax.
Only pull in flex if base version is too old.
Be more selective for which OSVERSIONS we need gcc due to the clang bug.

Obtained from:	Gstreamer upstream [1]

Add NO_STAGE all over the place in preparation for the staging support (cat:
graphics)

Add Gstreamer 1.0.7. This is the new stable version of the
Gstreamer multimedia framework.

Use the USE_GSTREAMER1 macro to select Gstreamer 1.0 plugins. A new chapter
for the porters handbook about gstreamer is a work in progress.

X related plugins are now stand alone. The gio plugin is now part of the
gstreamer1-plugins port and the oss plugins are now part of the
gstreamer1-plugins-good port.

Note that the pulseaudio plugin is missing because it needs a newer version
of pulseaudio. Also there are still a number of plugins from -bad which
haven't been ported to the 1.0 API yet.