RFR: 8278980: Update to 613.1 version of WebKit

[Ambarish Rapte]

Update JavaFX WebKit to GTK WebKit 2.34 (613.1).

Verified the updated version build, tests run and sanity testing.
This does not cause any issues except a unit test failure `IrresponsiveScriptTest`.
It is recorded and ignored using [JDK-8280421](https://bugs.openjdk.java.net/browse/JDK-8280421)

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Commit messages:
 - webkit update 613.1

Changes: https://git.openjdk.java.net/jfx/pull/723/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=723&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8278980
  Stats: 413083 lines in 6742 files changed: 231443 ins; 135747 del; 45893 mod
  Patch: https://git.openjdk.java.net/jfx/pull/723.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/723/head:pull/723

PR: https://git.openjdk.java.net/jfx/pull/723