Fix keybind conflicts (atom mac/linux default) (#13988)

- atom(mac): Cmd+j conflicts with `workspace: ToggleBottomDock` in
default map. Revert.
- default(linux): `ctrl-shift-t` conflict. Move
`project_symbols::Toggle` to `ctrl-t` to match vscode linux. Leave
`pane::ReopenClosedItem` at `ctrl-shift-t` to match vscode/chrome on
linux.
- Fixes #13973