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

assets/keymaps/default-linux.json

@@ -650,8 +650,8 @@
       "right": "outline_panel::ExpandSelectedEntry",
       "alt-copy": "outline_panel::CopyPath",
       "ctrl-alt-c": "outline_panel::CopyPath",
-      "alt-shift-copy": "outline_panel::CopyRelativePath",
-      "alt-ctrl-shift-c": "outline_panel::CopyRelativePath",
+      "alt-shift-copy": "workspace::CopyRelativePath",
+      "alt-ctrl-shift-c": "workspace::CopyRelativePath",
       "alt-ctrl-r": "outline_panel::RevealInFileManager",
       "space": "outline_panel::Open",
       "shift-down": "menu::SelectNext",
@@ -679,8 +679,8 @@
       "ctrl-v": "project_panel::Paste",
       "alt-copy": "project_panel::CopyPath",
       "ctrl-alt-c": "project_panel::CopyPath",
-      "alt-shift-copy": "project_panel::CopyRelativePath",
-      "alt-ctrl-shift-c": "project_panel::CopyRelativePath",
+      "alt-shift-copy": "workspace::CopyRelativePath",
+      "alt-ctrl-shift-c": "workspace::CopyRelativePath",
       "enter": "project_panel::Rename",
       "f2": "project_panel::Rename",
       "backspace": ["project_panel::Trash", { "skip_prompt": false }],