RFR: 8283218: Update GStreamer to 1.20.1 [v5]

[Alexander Matveev]

> - GStreamer updated to 1.20.1 and GLib updated to 2.72.0.
> - No changes to our code, except in GstAudioSpectrum.cpp g_atomic_pointer_compare_and_exchange() was changed to g_atomic_pointer_set(). For some reason I was not able to get code compiled with g_atomic_pointer_compare_and_exchange() used from C++ code. Also, I do not see a need to use g_atomic_pointer_compare_and_exchange(), since m_pHolder always equals to old_holder.
> - Tested on all platforms with all supported media streams.

Alexander Matveev has updated the pull request incrementally with one additional commit since the last revision:

  8283218: Update GStreamer to 1.20.1 [v5]

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Changes:
  - all: https://git.openjdk.java.net/jfx/pull/768/files
  - new: https://git.openjdk.java.net/jfx/pull/768/files/a29cd34b..39f0b050

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=768&range=04
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=768&range=03-04

  Stats: 1 line in 1 file changed: 1 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/jfx/pull/768.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/768/head:pull/768

PR: https://git.openjdk.java.net/jfx/pull/768