Update JavaFX WebKit to GTK WebKit 2.38 (615.1). Verified the updated version build, sanity tests and stability. This does not cause any issues except one unit test failure. Also, there are some artifacts observed while playing youtube
The above issues are recorded and ignored using below bugs: [JDK-8300954](https://bugs.openjdk.org/browse/JDK-8300954) [JDK-8301022](https://bugs.openjdk.org/browse/JDK-8301022) ------------- Commit messages: - Update Webkit to v615.1 Changes: https://git.openjdk.org/jfx/pull/1011/files Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1011&range=00 Issue: https://bugs.openjdk.org/browse/JDK-8299977 Stats: 197124 lines in 5579 files changed: 116283 ins; 42814 del; 38027 mod Patch: https://git.openjdk.org/jfx/pull/1011.diff Fetch: git fetch https://git.openjdk.org/jfx pull/1011/head:pull/1011 PR: https://git.openjdk.org/jfx/pull/1011
