Implement cross browser copy + paste

[nikku]

Turns this example into a module that implements cross browser copy + paste, utilizes the system clipboard (text) to transport the tree, works across different browsers, and browser tabs.

Demo

Showing copy and paste across Chrome and Firefox (two tabs):

Tasks

• Validate basic use of copy and paste from within user copy / paste context (using event.clipboardData)
• Verify this works with extensions
• Verify how pasting non-existing extension elements behaves
• Investigate whether we should use navigator.clipboard instead

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Relies on fixed versions of diagram-js (bpmn-io/diagram-js#660, bpmn-io/diagram-js#659) and bpmn-js (bpmn-io/bpmn-js#1707) to work.

Closes #2

[Handsome1337]

Why is it draft? Can I use it?

[nikku]

Why is it draft? Can I use it?

Did you try it? Did it work?

[Handsome1337]

Did you try it? Did it work?

I did not try. Turns out that I need extra copy logic (need to copy extra arguments and item definitions with ioSpecification) so I'm writing my own module. But it's still interesting to me why it's not merged

[nikku]

@Handsome1337 Probably worth to revisit this PR, since this is there, at last.

[nikku]

Updated for bpmn-js@18.10.1, attached you find a demo to see things working: