RFR: 8352162: Update libxml2 to 2.13.6 [v5]

[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:

  clean files , they do not require

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Changes:
  - all: https://git.openjdk.org/jfx/pull/1785/files
  - new: https://git.openjdk.org/jfx/pull/1785/files/1ea01cc1..0dbc2e96

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jfx&pr=1785&range=04
 - incr: https://webrevs.openjdk.org/?repo=jfx&pr=1785&range=03-04

  Stats: 2012 lines in 3 files changed: 0 ins; 2012 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