Add XSD for Log4j version 2.25.4

[vy]

Using apache/logging-log4j-tools#210, generated an XSD for apache/logging-log4j2@0628e53b (i.e., rel/2.25.4 tag).

[ppkarwasz]

Hi @vy,

Thank you for doing this. I compared this generated XSD with the one for 2.23.1 and there are some unexpected differences:

• The plugins from log4j-1.2-api are gone and are replaced from plugins in the log4j-1.2-api suite. Probably the main plugin descriptor has been overwritten by the test one.
• The schema of the Rfc5424Layout does not contain the newLineEscape and other properties that we brought back. On the other hand, those properties are in the 2.23.1 schema (go figure why…).

However, at least the booleans are back! 💯

[vy]

@ppkarwasz, I've updated the XSD in 17e8608. Would you mind checking it, please?

[ppkarwasz]

LGTM: the plugins from log4j-1.2-api are still missing, but let's merge this PR and worry about that later.

Only a couple of layouts in log4j-1.2-api might be useful to users.

[vy]

We've decided to postpone the XSD fix until 2.26.0 release.