add function to copy all function name

[FFengIll]

For convenience , I wish to add a button (or something else) to copy the symbol list from panel node.

May I do a PR for it?

[patrys]

I think you could add a context menu (IIRC it's already supported in the stable API) with "Copy symbol name". Can't comment on how to access the clipboard as I don't have the full API memorized.

[KamasamaK]

I don't believe there is anything in the VS Code API for accessing the clipboard, but you should be able to use a Node package like clipboardy to accomplish that.