Add Events Sheet Indent Scale preference.

[cyraid]

Description

Add a preference Indent Scale in the preferences dialog that controls the amount of scale (multiplying indent width) for the Events Sheet Control.

Background

My friend asked me if I could add an indent level setting as an extension, and after viewing the code it was not possible (as the indent is controlled with a hardcoded value). I thought a simple slider would fit the simplicity model of GDevelop. What do you guys think?

Screenshots

In the Events Sheet

This screenshot is using 3x indent scale.

In the Preferences Dialog

[cyraid]

@4ian My friend would sure love to use this as I did it for him, but he wants it officially in the editor. Thoughts? :)

[4ian]

I think that's an interesting setting :) Could you replace it with maybe a dropdown (SelectField)? We've never used the field you chose in material ui and I think for consistency with the rest of the app it might be just simpler to have something like:

Indent scale in Events Sheet : [ 2x ⌄]

[cyraid]

@4ian Hi Florian! I'm glad you think it's interesting as well! I'm not sure if you wanted the combo box on the right of the label, seeing as you wrote it like <label>: [ 2x v ] and the square brackets being the box. Let me know if you'd like me to change it or keep like the screenshot below.

New Screenshot

[ClementPasteau]

Closing this PR in favor of #6671 - had to do a few fixes in the PR regarding typing and formatting and couldn't push on your master branch :)