[FFe] Packaged VisualVM version (2.1.6) in Noble beta is incompatible with default java version (21)

[Why It is necessary]
VisualVM 2.1.6 is not compatible with Java 21:

Installing VisualVM via the apt on noble beta automatically installs java 21, but the packaged version of VisualVM (2.1.6) only supports Java 20 and below. When you try to launch it, you get a pop up message stating:

"You are running VisualVM using an unsupported Java version: 21.

Please use JDK 8 to JDK20 to run VisualVM. For more information about requirements and setup visit https://visualvm.github.io."

We need to upgrade to visualvm 2.1.8 to include support for Java 21 (default JDK) and Java 22 (shipped with Noble).

[Changelog]

 - Release 2.1.7[1]
 - Release 2.1.8[2]

[Build]

PPA: ppa:vpa1977/visualvm[3]

Build log[4]

[Testing]
- lintian:
P: visualvm source: maintainer-desktop-entry [debian/visualvm.desktop]
P: visualvm source: maintainer-manual-page [debian/visualvm.1]
- piuparts test[5]
- smoke test (profile tomcat).
  - launched visualvm
  - started tomcat instance
  - profiled tomcat cpu usage[6][7]

[Where the problems can occur]

visualvm is a leaf package with no reverse dependencies.
Current version (2.1.6) can not be run by default-jdk.

Upstream visualvm depends on netbeans platform 19, where noble has 18 packaged.
This will make plugins that require specific versions of netbeans API uninstallable:
 - VisualVM-Coherence: this plug-in provides a GUI to allow developers to view information about a running Coherence Cluster.
 - VisualVM-JFR Streaming: support for Java Flight Recorder event streaming.

[Original Description]
Installing VisualVM via the apt on noble beta automatically installs java 21, but the packaged version of VisualVM (2.1.6) only supports Java 20 and below. When you try to launch it, you get a pop up message stating:

"You are running VisualVM using an unsupported Java version: 21.

Please use JDK 8 to JDK20 to run VisualVM. For more information about requirements and setup visit https://visualvm.github.io."

From that website, I see that version 2.1.7 is required for Java 21 support (and a newer 2.1.8 release adds Java 22 support).

ProblemType: Bug
DistroRelease: Ubuntu 24.04
Package: visualvm 2.1.6-1
ProcVersionSignature: Ubuntu 6.8.0-11.11-generic 6.8.0-rc4
Uname: Linux 6.8.0-11-generic x86_64
ApportVersion: 2.28.0-0ubuntu1
Architecture: amd64
CasperMD5CheckResult: pass
CurrentDesktop: ubuntu:GNOME
Date: Thu Apr 4 15:30:22 2024
InstallationDate: Installed on 2024-03-26 (10 days ago)
InstallationMedia: Ubuntu 24.04 LTS "Noble Numbat" - Daily amd64 (20240323)
PackageArchitecture: all
RebootRequiredPkgs: Error: path contained symlinks.
SourcePackage: visualvm
UpgradeStatus: No upgrade log present (probably fresh install)

[1] https://bugs.launchpad.net/ubuntu/+source/visualvm/+bug/2060246/comments/2
[2] https://bugs.launchpad.net/ubuntu/+source/visualvm/+bug/2060246/comments/3
[3] https://launchpad.net/~vpa1977/+archive/ubuntu/visualvm
[4] https://launchpad.net/~vpa1977/+archive/ubuntu/visualvm/+sourcepub/15970292/+listing-archive-extra
[5] https://bugs.launchpad.net/ubuntu/+source/visualvm/+bug/2060246/comments/4
[6] https://salsa.debian.org/java-team/visualvm/uploads/d35f4b7d8ddaddbeccfeaae6fe66a2cb/image.png
[7] https://salsa.debian.org/java-team/visualvm/uploads/225d966fd9caca510951051d7006b319/image.png