RFR: 8283328: Update libxml2 to 2.9.13

[Kevin Rushforth]

On Thu, 31 Mar 2022 14:47:32 GMT, Hima Bindu Meda <hmeda at openjdk.org> wrote:

> 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.

I'll do testing and a sanity check review tomorrow. Here are three meta issues:

1. As noted in [SKARA-1222](https://bugs.openjdk.java.net/browse/SKARA-1222), your patch introduces a sym-link that is causing jcheck to throw an exception. Given that we do not want any sym-links in the repo anyway, you will need to revert the file in question.
2. Once the above is fixed, you will note that jcheck reports some whitespace errors.
3. You need to update the version in [libxml2.md](https://github.com/openjdk/jfx/blob/f169dde501c58fe107ab6da7f35667efb4992b65/modules/javafx.web/src/main/legal/libxml2.md).

4. I see that the following files were deleted as part of this PR. Was this intentional?

D       modules/javafx.web/src/main/native/Source/ThirdParty/libxml/src/AUTHORS
D       modules/javafx.web/src/main/native/Source/ThirdParty/libxml/src/ChangeLog
D       modules/javafx.web/src/main/native/Source/ThirdParty/libxml/src/README

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