Centralize the `CopyPath` and `CopyRelativePath` actions to `zed_actions` (#24836)

I spent an hour with @marcospb19 this morning debugging an issue with
adding `Copy Path` and `Copy Relative Path` actions to the editor
context menu. Turned out that the problem was using
`workspace::CopyPath` in the menu and `editor::CopyPath` in the action
handler.

This is an easy mistake to make, so let's fix it for everyone.

Release Notes:

- N/A