feat(zoom-scroll): config to disable requiring focus

[RedMser]

Proposed Changes

Adds a zoomScroll config option needsFocus. When set to false, focus of the canvas is no longer required to zoom/scroll. The default value is true, thus retaining the previous behavior.

Context: We have an app consisting of a full-screen BPMN modeler with a properties panel next to it. After clicking into the properties panel, users should not need to click on the modeler again to allow scrolling/zooming in it.

I've tested this patch in our app, to confirm that it works as expected.

Checklist

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• Contribution meets our definition of done
• Pull request establishes context
  • Link to related issue(s), i.e. Closes {LINK_TO_ISSUE} or Related to {LINK_TO_ISSUE}
  • Brief textual description of the changes
  • Screenshots or short videos showing UI/UX changes (not really applicable)
  • Steps to try out, i.e. using the @bpmn-io/sr tool (since the new default is backwards-compatible with old behavior, you'd need to add zoomScroll: { needsFocus: false } to the config)

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