RFR: 8340322: Update WebKit to 620.1

[Jay Bhaskar]

Webkit JavaFx upgrade from 619.1 to 620.1 <br>
Build is verified in mac , windows and linux. Sanity testing looks fine. No issues seen, except one observed CanvasPattern test where it works only on Linux but failed on Mac/Windows (WIP).
Windows build is using clang-cl compiler because Webkit has dropped MSVC compiler support.

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

Commit messages:
 - Webkit 2.46.5 upgrade

Changes: https://git.openjdk.org/jfx/pull/1703/files
  Webrev: Webrev is not available because diff is too large
  Issue: https://bugs.openjdk.org/browse/JDK-8340322
  Stats: 773682 lines in 8157 files changed: 644444 ins; 72180 del; 57058 mod
  Patch: https://git.openjdk.org/jfx/pull/1703.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1703/head:pull/1703

PR: https://git.openjdk.org/jfx/pull/1703