RFR: 8377930: Additional WebKit 623.1 fixes from WebKitGTK 2.50.5

[Hima Bindu Meda]

This PR updates webkit to v2.50.5. Verified build and stability on all platforms. No issue seen.

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Commit messages:
 - additional webkit fixes from webkit-2.50.5

Changes: https://git.openjdk.org/jfx/pull/2089/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=2089&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8377930
  Stats: 862 lines in 97 files changed: 474 ins; 141 del; 247 mod
  Patch: https://git.openjdk.org/jfx/pull/2089.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/2089/head:pull/2089

PR: https://git.openjdk.org/jfx/pull/2089