Guard Copy action when ClipboardItem is missing

[schickling]

Summary

• add feature detection before instantiating ClipboardItem
• fall back to navigator.clipboard.writeText for browsers that do not expose the constructor (e.g. Firefox/Safari)
• keep existing behaviour for browsers that support ClipboardItem

Testing

• Verified the Copy Page button in a local Starlight site on Firefox 130

[reynaldichernando]

thanks for the PR!
please give me some time to test this, since i don't have firefox installed, plus to make sure it doesn't break on other browser

safari is notoriously hard to do copy to clipboard

[reynaldichernando]

quick update on the PR: this breaks copy in safari
let me have a look on how to do this properly while still supporting the navigator fallback