The event passed to graph.on callback has incorect typing (IG6GraphEvent) #2724

• I have searched the issues of this repository and believe that this is not a duplicate.

Reproduction link

Steps to reproduce

1. Use Typescript
2. Subscribe to keydown or node:mousedown event
3. Click on a node or press a key
4. evt.target.isCanvas function is specified as available from type definitions but it is not, since those events are either GraphEvent or KeyboardEvent, but not IG6GraphEvent

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