This increase the safety of our build; external consumers
do no longer need to account for the `browser` field to
bundle bpmn-js (or otherwise bundle a Node shim, unintentionally).
This covers two scenarios:
1. When a shape is replaced with an expanded subprocess
2. When a subprocess is toggled from collapsed to expanded
Only when:
1. There are incoming sequence flows (previous content)
2. There are no outgoing sequence flows (following content)
Handles two new scenarios:
1. A user wants to connect an event-based gateway to an event-based
gateway target with existing incoming sequence flows. The existing
sequence flows are removed before connecting the new one.
2. A user wants to replace a gateway, that is already connected to
event-based gateway targets, with an event-based gateway. The existing
incoming sequence flows of the targets, which do not belong to the
newly replaced event-based gateway, are removed before the replacement
operation finishes.
This is because target elements in an event gateway configuration
must not have any additional incoming sequence flows other than
that from the event gateway.
