ENA-83: Ability to Zoom In and Zoom Out responsively

Expected Behavior

In the browser version of Scratch, it's possible to Zoom In and Zoom Out responsively, as via command-plus and command-minus on a Mac, whereby the entire UI resizes (not just the code area).

We use such when teaching on a projector (zooming in 150% typically), so as to make UI elements more visible, particularly for students farther back.

Actual Behavior

As best I can tell on the desktop version, there might not be a similar feature, unless it's another set of keyboard shortcuts?

By contrast, Electron apps like VS Code desktop do to resize with command-{plus,minus}, per https://github.com/microsoft/vscode/blob/main/src/vs/platform/window/electron-sandbox/window.ts. And a manual workaround (e.g., for a teacher in class) seems to be executing document.body.style.zoom = '150%' in Electron's dev tools

Steps to Reproduce

1. Install https://scratch.mit.edu/download for macOS.
2. Launch Scratch desktop app.
3. Try to zoom in/out with command-{plus,minus}.

System Details

macOS 12.5.1, Scratch desktop 3.29.1.

Screenshots

Browser version, zoomed in

Desktop version, not zoomed in

Thank you!

CC @rongxin-liu @carterzenke

Start by tracing the macOS keyboard-shortcut and window handling in the desktop app, using the referenced VS Code window.ts as a comparison. Verify the existing document.body.style.zoom workaround in Electron dev tools, then make command-plus and command-minus resize the entire UI responsively and confirm both zoom directions manually on macOS.