RFR: 8352162: Update libxml2 to 2.13.6 [v2]

[Jay Bhaskar]

> As part of the current WebKit JFX  upgrade, it is required to update libxml and libxslt to compatible versions. Additionally, this release addresses several known issues from the previous version to improve stability and performance.

Jay Bhaskar has updated the pull request incrementally with one additional commit since the last revision:

  remove un-needed files

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1785/files
  - new: https://git.openjdk.org/jfx/pull/1785/files/38f16895..fc549b02

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1785&range=01
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1785&range=00-01

  Stats: 6001 lines in 9 files changed: 0 ins; 6001 del; 0 mod
  Patch: https://git.openjdk.org/jfx/pull/1785.diff
  Fetch: git fetch https://git.openjdk.org/jfx.git pull/1785/head:pull/1785

PR: https://git.openjdk.org/jfx/pull/1785