[FR] Inline editor to fix template issues

[michaelrog]

For errors in Twig templates, it'd be dope if the dev can open a code editor right from the error page, and Cmd-S to save, which writes the change to disk and reloads the page.

• For front-end templates (i.e. not CP/Craft/plugin templates)
• if the user is logged in Admin
• only in Dev Mode.

[michaelrog]

Monaco editor (a web version of the VSCode editor): https://github.com/Microsoft/monaco-editor