RFR: 8352162: Update libxml2 to 2.13.6 [v3]

[Jay Bhaskar]

> The upgrade is required to address 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 some non required files and update to 2.13.8

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

Changes:
  - all: https://git.openjdk.org/jfx/pull/1785/files
  - new: https://git.openjdk.org/jfx/pull/1785/files/fc549b02..19ede147

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1785&range=02
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1785&range=01-02

  Stats: 25488 lines in 27 files changed: 3894 ins; 21584 del; 10 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