Fix cmd-n in the project panel context menu and bind global workspace actions (#3491)

This PR binds the `workspace::NewFile` action only in the `Workspace`
context. It previously was bound globally, which caused us to hijack the
`cmd-n` binding when the context menu was visible in the project panel.
In the process, we also added some other global workspace actions and
move some other global bindings to be bound only on `Pane` and
`Workspace`.

Release Notes:

- N/A