Add support for cross-origin cross-tab copy and paste

[gonfunko]

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Component

cross-tab copy paste

Problem

No response

Request

The cross-tab copy-paste plugin currently only works for sites on the same domain, since it uses localstorage to persist serialized blocks, which has a same origin policy enforced by the browser. It would be nice if it were possible to copy blocks across domains; most likely this would require coordination/allowlisting specific domains and communicating over postMessage, but it should in theory be possible as an additional option. One usecase (staging vs prod environments) was outlined here: https://groups.google.com/g/blockly/c/qK_jP9mG_pw.

Alternatives considered

• Consider using system clipboard using old tricks to copy with a hidden text field
• Consider using new clipboard web apis

Additional context

No response

[TannerGabriel]

I actually had an implementation that used the system clipboard in one of my projects, which seems to fix the issue here as well. I submitted a PR, so let me know if this is what you had in mind. If not, feel free to close it.