RFR: 8281711: Cherry-pick WebKit 613.1 stabilization fixes

[Ambarish Rapte]

Include additional stabilization fixes of WebKit 613.1
Sanity testing did not show any concerns.

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Commit messages:
 - Cherry-pick WebKit 613.1 stabilization fixes

Changes: https://git.openjdk.java.net/jfx/pull/733/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=733&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281711
  Stats: 1219 lines in 127 files changed: 767 ins; 169 del; 283 mod
  Patch: https://git.openjdk.java.net/jfx/pull/733.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/733/head:pull/733

PR: https://git.openjdk.java.net/jfx/pull/733