Support ad-hoc subprocesses

[saig0]

What should we do?

In C8 BPMN editor

• I can add an ad-hoc subprocess for the execution platform 8.7 and don't see a linting error
• I can set the FEEL expression activeElementsCollection on an ad-hoc subprocess

The activeElementsCollection attribute

• Only for ad-hoc processes
• Optional, can be empty
• Must be a FEEL expression
• Description: Return a list of BPMN element ids that should be activated when entering the ad-hoc subprocess.
• XML path: bpmn:adHocSubProcess > bpmn:extensionElements > zeebe:adHoc > activeElementsCollection

XML representation

    <bpmn:adHocSubProcess id="Activity_1kaluzl">
      <bpmn:extensionElements>
        <zeebe:adHoc activeElementsCollection="=activeElements" />
      </bpmn:extensionElements>
      <bpmn:incoming>Flow_1qw4w9y</bpmn:incoming>
      <bpmn:outgoing>Flow_1e61rhe</bpmn:outgoing>
      <bpmn:serviceTask id="Activity_1762pvi" name="A">
        <bpmn:extensionElements>
          <zeebe:taskDefinition type="A" />
        </bpmn:extensionElements>
      </bpmn:serviceTask>
      <bpmn:serviceTask id="Activity_036tbyz" name="B">
        <bpmn:extensionElements>
          <zeebe:taskDefinition type="B" />
        </bpmn:extensionElements>
      </bpmn:serviceTask>
    </bpmn:adHocSubProcess>

BPMN example

Why should we do it?

Child of https://github.com/camunda/product-hub/issues/2546

[barmac]

Thanks for opening the issue! I will put it to the backlog for now but we will keep it in mind for the future planning.
Actually, ready is a better place given the state of the linked epic.