feat(templates): client-Java process handlers for template-bpm (#6584)

[delchev]

Closes #6584. Part of the umbrella #6591.

The BPM starter was the last template wired to the TypeScript stack:

1. tasks/my-service-task.ts → <package>/MyServiceTask.java, a plain
   org.flowable.engine.delegate.JavaDelegate (instantiated per execution via its no-arg
   constructor — not a bean, as DirigibleJavaCallDelegate requires).
2. process.bpmn.template's service task switches from ${JSTask} + a .ts handler path to
   ${JavaTask} + a handler field holding the class' FQN (${javaPackageName}.MyServiceTask).
3. api/ProcessService.ts.template → <package>/ProcessService.java, an sdk.http @Controller
   starting the process through sdk.bpm.Process, at
   POST /services/java/<project>/<package>/ProcessService/processes with the process variables as
   its JSON body.
4. Logging goes through sdk.log.Logging.

The .gen descriptor already pointed at template-form-builder-harmonia (repointed when the
AngularJS templates were removed); the issue's last form-builder-angularjs mention lives in the
form-builder README and is reworded, so grep -rn "form-builder-angularjs" components/template is
now empty.

Note the templates render through Velocity, so the Java sources use ${javaPackageName} /
${processId}, not {{…}} — and ${JavaTask} survives verbatim because it is an undefined
reference, the same mechanism ${JSTask} relied on.

Verification (scaffolded, published, run on a live instance)

POST /services/java/demobpm/demobpm/ProcessService/processes  {"greeting":"hi"}
→ {"processInstanceId":"13","processKey":"demoprocess",…}

app.demobpm.MyServiceTask - Hello World! Process instance [13] with variables: {greeting=hi}

The service task ran through the Java delegate (no JS-delegate fallback in the log), the generated
files land at <package>/{ProcessService,MyServiceTask}.java, and the Problems view is clean.

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