Cannot use context menu with keyboard

[barmac]

Describe the Bug

The context menu does not take the focus and I cannot take any action in it with keyboard.

How to open context menu with keyboard on Mac (thanks @lmbateman): https://support.apple.com/en-gb/guide/mac-help/mh27469/mac

Steps to Reproduce

1. Open context menu.
2. Try to move around with arrow keys.

Expected Behavior

Context menu should work exactly like a system context menu:

• Be a focus trap
• Change selection with arrow keys
• Select and perform action with enter

It closes with escape or outside click already, which otherwise would have been another requirement.

Environment

Please complete the following information:

• Browser: [e.g. IE 11, Chrome 69]
• OS: [e.g. Windows 7]
• Library version: [e.g. 2.0.0]

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Child of https://github.com/bpmn-io/internal-docs/issues/909