RFR: 8254836: Cherry pick GTK WebKit 2.30.3 changes

[Arun Joseph]

Update to GTK WebKit 2.30.3
https://webkitgtk.org/2020/11/20/webkitgtk2.30.3-released.html

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Commit messages:
 - 8254836: Cherry pick GTK WebKit 2.30.3 changes

Changes: https://git.openjdk.java.net/jfx/pull/392/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=392&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8254836
  Stats: 679 lines in 37 files changed: 483 ins; 87 del; 109 mod
  Patch: https://git.openjdk.java.net/jfx/pull/392.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/392/head:pull/392

PR: https://git.openjdk.java.net/jfx/pull/392