RFR: 8283328: Update libxml2 to 2.9.13 [v2]

[Hima Bindu Meda]

> We currently use libxml2 version 2.9.12. It should be updated to latest stable release, which is version 2.9.13.
> The steps to update libxml are documented in UPDATING.txt.
> There is compilation issue with the release 2.9.13, as mentioned here: https://gitlab.gnome.org/GNOME/libxml2/-/issues/349.
> Updated the code with the changes as per the fix mentioned in above link.
> 
> Compiled and verified on Windows, Mac and Linux platforms.
> Sanity testing looks fine.

Hima Bindu Meda has updated the pull request incrementally with one additional commit since the last revision:

  Add README.md and update libxml2.md

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

Changes:
  - all: https://git.openjdk.java.net/jfx/pull/764/files
  - new: https://git.openjdk.java.net/jfx/pull/764/files/8dca3c2e..92ba9af0

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jfx&pr=764&range=01
 - incr: https://webrevs.openjdk.java.net/?repo=jfx&pr=764&range=00-01

  Stats: 28 lines in 2 files changed: 27 ins; 0 del; 1 mod
  Patch: https://git.openjdk.java.net/jfx/pull/764.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/764/head:pull/764

PR: https://git.openjdk.java.net/jfx/pull/764