RFR: 8332539: Update libxml2 to 2.12.7

[Hima Bindu Meda]

Updated libxml to v2.12.7. Sanity testing looks fine. No issue seen

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Commit messages:
 - configure libxml on windows
 - configure libxml on linux
 - update libxml to v2.12.7

Changes: https://git.openjdk.org/jfx/pull/1464/files
  Webrev: https://webrevs.openjdk.org/?repo=jfx&pr=1464&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/jfx/pull/1464.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1464/head:pull/1464

PR: https://git.openjdk.org/jfx/pull/1464