RFR: 8306806: JMX agent with JDP enabled won't start when PerfData is disabled [v2]

[Kevin Walls]

> Java Discovery Protocol (perhaps a hidden feature, but maybe should be more widely known!) and -XX:-UsePerfData together cause a failure to startup.
> 
> PerfData is the mechanism for communicating the URL and other properties for remote management, so disabling PerfData clearly breaks this.  But there should be a clearer message, and not a fatal error.
> 
> e.g.
> $ java -XX:-UsePerfData  -Dcom.sun.management.jmxremote.autodiscovery=true -Dcom.sun.management.jmxremote.port=0 -Dcom.sun.management.jmxremote.authenticate=false -Dcom.sun.management.jmxremote.ssl=false --version
> Warning: Exception thrown by the agent : JDP not starting, PerfData not available: Empty PerfData buffer
> java 21-internal 2023-09-19 LTS
> ...etc...
> 
> The use of PerfData is superior to the previous hard-coding of knowledge of the URL protocol and structure, and is required to communicate a dynamically assigned port (JDK-8167337).

Kevin Walls has updated the pull request incrementally with two additional commits since the last revision:

 - undo (C)
 - Handle BufferUndeflowException to leave IOException free for other failures

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

Changes:
  - all: https://git.openjdk.org/jdk/pull/13928/files
  - new: https://git.openjdk.org/jdk/pull/13928/files/fa0fa449..4dcaf76d

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=13928&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=13928&range=00-01

  Stats: 7 lines in 2 files changed: 1 ins; 3 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/13928.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/13928/head:pull/13928

PR: https://git.openjdk.org/jdk/pull/13928