[jdk17] RFR: 8266614: update manpage for -Xlog:async

[David Holmes]

Please review this update to the java manpage to describe the new -Xlog:async flag

There are two places where the text is changed:

1. At the start where the -Xlog synopsis is given it now shows that `-Xlog:directive` is an allowed form where directive can be one of: help, disable, async
2.  A new subsection "-Xlog Output Mode" that explains async mode

The commited file is the java.1 nroff version which is not very readable, so I've included a commit that also contains a html version with the changed text flagged by "START NEW TEXT" and "END NEW TEXT". You can view that in rendered html via this link:

https://htmlpreview.github.io/?https://github.com/openjdk/jdk17/blob/8dcf544dfd2e19a3a49cce98d2d9abd9d2756538/java.html

Note that because the nroff file has not been updated for a while it also contains changes unrelated to this PR, the source changes for which have already been reviewed and approved. So just ignore those bits and look at the html file.

Thanks,
David

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

Commit messages:
 - Removed java.html again
 - Temporary commit to see changes in a readable form
 - 8266614: update manpage for -Xlog:async

Changes: https://git.openjdk.java.net/jdk17/pull/16/files
 Webrev: https://webrevs.openjdk.java.net/?repo=jdk17&pr=16&range=00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8266614
  Stats: 120 lines in 1 file changed: 38 ins; 78 del; 4 mod
  Patch: https://git.openjdk.java.net/jdk17/pull/16.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk17 pull/16/head:pull/16

PR: https://git.openjdk.java.net/jdk17/pull/16