RFR: 8320267: WebView crashes on macOS 11 with WebKit 616.1

[Kevin Rushforth]

With the help of debug build which pinpointed the crash, I found the commit in upstream WebKit core that caused the crash. That commit was subsequently reverted not long after it was initially committed. This reverted commit wasn't in the stabilization branch we picked up for WebKit 616.1. It will be in the next WebKit update, but we need a fix sooner than that.

The proposed fix is to cherry-pick the commit that reverts the problematic commit: https://github.com/WebKit/WebKit/commit/d6d61bb1b76bbac53b403d217428e65a12c4e2e3

I've done an initial sanity test run on all platforms.

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Commit messages:
 - 8320267: WebView crashes on macOS 11 with WebKit 616.1

Changes: https://git.openjdk.org/jfx/pull/1297/files
 Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1297&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8320267
  Stats: 191 lines in 2 files changed: 15 ins; 171 del; 5 mod
  Patch: https://git.openjdk.org/jfx/pull/1297.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1297/head:pull/1297

PR: https://git.openjdk.org/jfx/pull/1297