[jfx17u] RFR: 8331748: Update libxml2 to 2.12.6

[Johan Vos]

8331748: Update libxml2 to 2.12.6

-------------

Commit messages:
 - Backport 97b1402501983f121f75c24a510f466837fa2ecc

Changes: https://git.openjdk.org/jfx17u/pull/190/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx17u&pr=190&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8331748
  Stats: 24912 lines in 115 files changed: 8485 ins; 11207 del; 5220 mod
  Patch: https://git.openjdk.org/jfx17u/pull/190.diff
  Fetch: git fetch https://git.openjdk.org/jfx17u.git pull/190/head:pull/190

PR: https://git.openjdk.org/jfx17u/pull/190