[jfx11u] Integrated: 8281711: Cherry-pick WebKit 613.1 stabilization fixes

[Kevin Rushforth]

Clean backport to `jfx11u`. I tested this along with the other VS 2019 and WebKit 613.1 fixes together in the `test-kcr-11.0.15` branch.

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Commit messages:
 - 8281711: Cherry-pick WebKit 613.1 stabilization fixes

Changes: https://git.openjdk.java.net/jfx11u/pull/79/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=79&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8281711
  Stats: 1218 lines in 127 files changed: 767 ins; 169 del; 282 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/79.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/79/head:pull/79

PR: https://git.openjdk.java.net/jfx11u/pull/79