[jfx18] RFR: 8283328: Update libxml2 to 2.9.13

[Johan Vos]

Reviewed-by: jvos, kcr, arapte

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Commit messages:
 - 8283328: Update libxml2 to 2.9.13

Changes: https://git.openjdk.java.net/jfx/pull/777/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jfx&pr=777&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8283328
  Stats: 55661 lines in 105 files changed: 5761 ins; 24999 del; 24901 mod
  Patch: https://git.openjdk.java.net/jfx/pull/777.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/777/head:pull/777

PR: https://git.openjdk.java.net/jfx/pull/777