[jfx24u] RFR: 8353916: Unexpected event type for DOM mutation events with WebKit 620.1

[Jay Bhaskar]

A clean backport to jfx24u , the patch fixes the mutation event typecast issue the change for supportig old style mutation event type.

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Commit messages:
 - Backport dc115d5862894953fb27c1f209b2d81d3694db70

Changes: https://git.openjdk.org/jfx24u/pull/17/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx24u&pr=17&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8353916
  Stats: 3 lines in 1 file changed: 3 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jfx24u/pull/17.diff
  Fetch: git fetch https://git.openjdk.org/jfx24u.git pull/17/head:pull/17

PR: https://git.openjdk.org/jfx24u/pull/17