Logging fixes around plugin disable and shutdown; logging cleanup (#13622)

This fixes a race where a late log message to the async appender could cause console reinitialization during shutdown

Also fixes issues when plugin log messages with classloader scoped context tries to print after the plugin classloader is closed by flushing the async appender as a part of disabling plugins.

Remove StacktraceDeobfuscator and ExtraClassInfoRewritePolicy

- Stacktrace deobfuscator has not been useful for a while and will be completely useless with MC 26.1
- ThrowableProxy is deprecated with no replacement in Log4j 2.25.0 and newer (getThrownProxy is no longer called by built in throwable formatters, so our code is already dead)