Add "Open External Terminal" action (like VS Code's Ctrl+Shift+C)

[oxijoined]

What are you proposing?

A new native action workspace::OpenExternalTerminal that opens the user's preferred external terminal application in the current project's working directory.

This is equivalent to VS Code's workbench.action.terminal.openNativeConsole (Ctrl+Shift+C).

The action would be bindable in keymap like any other action:

{
  "context": "Workspace",
  "bindings": {
    "ctrl-shift-c": "workspace::OpenExternalTerminal"
  }
}

Why does this matter?

Many workflows require a full-featured external terminal window — running Docker, using tmux sessions, debugging with specialized TUI tools, or simply preferring a specific terminal emulator over the built-in one.

Currently the only workaround is a verbose task::Spawn hack:

// keymap
"ctrl-shift-c": ["task::Spawn", { "task_name": "Open PowerShell here" }]

// tasks.json
{
  "label": "Open PowerShell here",
  "command": "pwsh",
  "args": ["-Command", "Start-Process pwsh -ArgumentList '-NoExit','-Command','Set-Location \"$ZED_WORKTREE_ROOT\"'"],
  "reveal": "never",
  "hide": "always"
}

This is fragile, platform-specific, non-discoverable, and requires users to maintain task definitions just to open a terminal. A native action would make this a one-line keymap binding.

Are there any examples or context?

VS Code has this as a built-in feature since its early versions:
- Command: workbench.action.terminal.openNativeConsole
- Default binding: Ctrl+Shift+C (Windows/Linux), ⇧⌘C (macOS)
- Configurable via terminal.external.windowsExec, terminal.external.osxExec, terminal.external.linuxExec
- Opens at workspace root directory

JetBrains IDEs also have "Open in Terminal" that launches an external terminal.

Possible approach

- Add a new action workspace::OpenExternalTerminal in the workspace crate
- Add a terminal settings field for the external terminal executable (per-platform defaults: cmd.exe/powershell on Windows, Terminal.app on macOS, x-terminal-emulator or xterm on Linux)
- The action spawns the configured terminal as a detached process with cwd set to the project's worktree root
- No default keybinding (users bind it themselves), or a default matching VS Code's convention
- Setting is user-level only (not project-level) for security — prevents malicious projects from specifying arbitrary executables

[rommyarb]

Duplicate of #7974