[FEAT] Add additional css classes to precisely select BPMN elements in the DOM

[tbouffard]

Is your feature request related to a problem? Please describe.
#921 introduce dedicated class name for each BPMN elements in the DOM based on the BPMN semantic.
For instance, userTask elements have the bpmn-user-task class.

Describe the solution you'd like
In addition to top-level BPMN types, we would like additional classes as part of #45 to be set for

• bpmn detection by kind/type: activities, tasks, events, ...
• related to sub-types
  • event definitions: timer, message, ...
  • subprocess: transaction, adhoc, ...
  • call activity calling a global task
• message flow icon initiating or not_initiating (after fixing #1622)
• event based gateway type (exclusive, parallel, ....).

This would also open new styling capabilities.

Additional context
The class can also help for rendering customization.