fix: editor discard prompt

[Zouizoui78]

Description
Currently the editor changes discard prompt is bugged and appears in the following two situations where it should not:

• when the file is empty, like right after its creation
• after the file has been saved

This PR aims to solve both issues.

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[Zouizoui78]

I changed my commit a bit (forced pushed because of a mistake on my part) to make use of the logic that is already implemented by ace to know if the editor is dirty or not.