[jfx21u] RFR: 8332539: Update libxml2 to 2.12.7

[Johan Vos]

8332539: Update libxml2 to 2.12.7

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Commit messages:
 - Backport dedcf1d236b5429dcf3c42f5fd1095b28d5da063

Changes: https://git.openjdk.org/jfx21u/pull/60/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx21u&pr=60&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8332539
  Stats: 67 lines in 9 files changed: 26 ins; 9 del; 32 mod
  Patch: https://git.openjdk.org/jfx21u/pull/60.diff
  Fetch: git fetch https://git.openjdk.org/jfx21u.git pull/60/head:pull/60

PR: https://git.openjdk.org/jfx21u/pull/60