[Terminal] Provide a command/action to open a new Terminal view (for keybinding and Quick Access)

## Problem

Currently, there is no Eclipse **command** (in the command/handler framework sense) to open a new Terminal view.
The only way to open a new terminal instance is via the monitor button inside the Terminal view itself.

This means:
- **No keyboard shortcut can be bound** to "Open New Terminal" via *Preferences > General > Keys*
- **Quick Access (Ctrl+3)** does not find an "Open New Terminal" action
- Users (like me) who rely on keyboard-driven workflows cannot quickly spawn a new terminal without first focusing the Terminal view and clicking the toolbar button :(

## Expected Behavior

A proper Eclipse `` (e.g., `org.eclipse.tm.terminal.view.ui.command.newTerminal`) with a default `` should be contributed so that:

1. Users can **bind a custom keyboard shortcut** to open a new terminal via *Preferences > General > Keys*
2. The action appears in **Quick Access (Ctrl+3)** when searching for "terminal"
3. The command works **regardless of whether the Terminal view is currently focused or even open**

I can fix this myself once I have time.

## Environment
- Eclipse IDE 2025-12 (4.38)
- OS: RHEL9
- Terminal Feature 1.0.100.v20260410-1244 org.eclipse.terminal.feature.feature.group

Start by locating the Terminal view's existing monitor-button action and the terminal command/handler contributions in the Eclipse Platform source. Add the new command so it is available without the view focused or open, then verify it appears in Preferences > General > Keys and Quick Access and opens a new Terminal view.

Written by the indexing model from the issue text.