RFR: 8278980: Update WebKit to 613.1 [v2]

[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)

Ambarish Rapte has updated the pull request incrementally with one additional commit since the last revision:

  Restore commits that were mistakenly reverted.
  
  8279013: ES2Pipeline fails to detect AMD vega20 graphics card
  8277853: With Touch enabled devices scrollbar disappears and the table is scrolled to the beginning
  8277122: SplitPane divider drag can hang the layout

-------------

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/723/files
  - new: https://git.openjdk.java.net/jfx/pull/723/files/b1cd88e7..ef730f84

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=723&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=723&range=00-01

  Stats: 121 lines in 5 files changed: 112 ins; 1 del; 8 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