RFR: 8347114: JMXServiceURL with null protocol defaults to jmxmp [v2]

[Kevin Walls]

> Remove the historic oddity that JMXServiceURL defaults to jmxmp if a null protocol is specified.
> 
> This has been the case for JMXServiceURL constructors that take individual parameters, but not for JMXServiceURL(String serviceURL), which enforces that there must be a protocol (If empty in the String, it throws: java.net.MalformedURLException: Missing or invalid protocol name: "")
> 
> A missing (null) protocol should throw a MalformedURLException for all constructors.
> 
> JMXMP was never part of the JDK, but a separate component in the historic JMX Remote reference implementation.
> 
> While we are here, remove the last remaining JMXMP references in the source:
> 
> src/java.management/share/classes/javax/management/remote/JMXConnectorServerMBean.java:     * (JMXMP Connector and RMI Connector).</p>
> src/java.management/share/classes/javax/management/remote/JMXConnectorServer.java:     * (JMXMP Connector and RMI Connector).</p>
> 
> These doc references are just examples of Connectors that support generation of client stubs.  There is no need for JMXMP to be mentioned here.

Kevin Walls has updated the pull request incrementally with one additional commit since the last revision:

  Add test

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Changes:
  - all: https://git.openjdk.org/jdk/pull/25674/files
  - new: https://git.openjdk.org/jdk/pull/25674/files/6ab3203c..83c153e5

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=25674&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=25674&range=00-01

  Stats: 58 lines in 1 file changed: 58 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk/pull/25674.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25674/head:pull/25674

PR: https://git.openjdk.org/jdk/pull/25674