[jfx18] RFR: 8282099: Cherry-pick WebKit 613.1 stabilization fixes (2)

[Johan Vos]

Reviewed-by: kcr, jvos

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Commit messages:
 - 8282099: Cherry-pick WebKit 613.1 stabilization fixes (2)

Changes: https://git.openjdk.java.net/jfx/pull/774/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=774&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8282099
  Stats: 186 lines in 11 files changed: 116 ins; 33 del; 37 mod
  Patch: https://git.openjdk.java.net/jfx/pull/774.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/774/head:pull/774

PR: https://git.openjdk.java.net/jfx/pull/774