`getAllElementsInProcess` does not get all elements in process if the process contains other subprocess variants

[buehlefs]

Current Behavior:

components/bpmn-q/modeler-component/editor/util/TransformationUtilities.js getAllElementsInProcess does not decend into adHocSubProcess elements (or other custom subprocess elements).

Expected Behavior:

the function should find instances in all kinds of subprocess elements

Steps to Reproduce:

call the function in a workflow containing different subprocess elements