Add Ribbon View, Demo Fold Provider, Ribbon Toggles

[thecoolwinter]

Description

Note

For reviewers, this is merging into the dev branch. These changes require the version of CETV in this PR. Please pull those changes locally and test using that.

Note

I'll be making some TODOs in the tracking issue #43 for things that aren't included here. Like the overlapping folds UI issue.

Adds the first version of the code folding ribbon, with a very basic folding model.

This is mostly a UI change. It includes changes to the gutter, and a new view for displaying folds. The model and related demo fold provider should be considered incomplete and only for demo purposes.

This also doesn't implement the hover state yet. Just a very basic outline of everything.

Things to review:

• New FoldingRibbonView
• New LineFoldingModel
• Changes in GutterView
• Changes to TextViewController
• Changes to CodeEditSourceEditor

Related Issues

• ✨ Code Folding #43

Checklist

• I read and understood the contributing guide as well as the code of conduct
• The issues this PR addresses are related to each other
• My changes generate no new warnings
• My code builds and runs on my machine
• My changes are all related to the related issue above
• I documented my code

Screenshots

Light mode.

Dark Mode.

Folds are transparent for scrolling text.