fix #6996 TOGGLE_MAXIMIZED overrides monaco tab capture

[caseyflynn-google]

What it does

Change modifies the default TOGGLE_MAXIMIZED keybinding from ctrl+m to
alt+m to ensure it does not overwrite a11y feature of Monaco "toggle tab
key moves focus".

How to test

1. Open Theia
2. Open a file for edit
3. Issue Ctrl+m

Observe pressing the tab key changes focus as opposed to sending a tab to the editor.

4. Focus the editor
5. Issue alt+m

Observe toggle maximize works as intended.

Review checklist

• as an author, I have thoroughly tested my changes and carefully followed the review guidelines

Reminder for reviewers

• as a reviewer, I agree to behave in accordance with the review guidelines

[akosyakov]

alt+m does not work for the focused terminal (tab highlighted with blueish bar) for me on ubuntu.It is the main use case to zoom in/out terminals.

@eclipse-theia/ecd-theia-committers Which shortcut could be better?

[marcdumais-work]

alt+m does not work for the focused terminal (tab highlighted with blueish bar) for me on ubuntu.It is the main use case to zoom in/out terminals.

Same for me on my Ubuntu 18.04-based laptop. However ctrl-m behaves the same for me on master, so not a new problem it seems.

[akosyakov]

let's try this keybinding