[jfx11u] RFR: 8268849: Update to 612.1 version of WebKit

[Kevin Rushforth]

Nearly clean backport of third-party update to WebKit 612.1. There was one minor conflict in one unit test file due to difference in context.

As an FYI, I tested this patch in my [test-kcr-11.0.13](https://github.com/kevinrushforth/jfx11u/tree/test-kcr-11.0.13) branch, which has the aggregate set of patches for the following bugs: [JDK-8211308](https://bugs.openjdk.java.net/browse/JDK-8211308), [JDK-8268915](https://bugs.openjdk.java.net/browse/JDK-8268915), [JDK-8269147](https://bugs.openjdk.java.net/browse/JDK-8269147), [JDK-8269131](https://bugs.openjdk.java.net/browse/JDK-8269131), [JDK-8268849](https://bugs.openjdk.java.net/browse/JDK-8268849), [JDK-8270479](https://bugs.openjdk.java.net/browse/JDK-8270479), [JDK-8272329](https://bugs.openjdk.java.net/browse/JDK-8272329).

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Commit messages:
 - 8268849: Update to 612.1 version of WebKit

Changes: https://git.openjdk.java.net/jfx11u/pull/34/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx11u&pr=34&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8268849
  Stats: 286061 lines in 5711 files changed: 175196 ins; 68118 del; 42747 mod
  Patch: https://git.openjdk.java.net/jfx11u/pull/34.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx11u pull/34/head:pull/34

PR: https://git.openjdk.java.net/jfx11u/pull/34