[GraphEditor] Rewrite AttributeItemDelegate with outside definitions for the components

[raphaelKoskas]

Description

This PR moves the definition of the components inside AttributeItemDelegate to AttributeControls, as externalised components, thus easing their use in a broader context than the GraphEditor.

Features list

• Rewrote the components in separated files

Implementation remarks

• ListAttribute and GroupAttribute have been left as is due to their high dependency on the attribute object.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 86.27%. Comparing base (643231f) to head (27772a9).
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@           Coverage Diff            @@
##           develop    #3177   +/-   ##
========================================
  Coverage    86.27%   86.27%           
========================================
  Files           81       81           
  Lines        12367    12367           
========================================
  Hits         10670    10670           
  Misses        1697     1697           

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• 📦 JS Bundle Analysis: Save yourself from yourself by tracking and limiting bundle sizes in JS merges.

[cbentejac]

Components are not, for the most part, fully attribute-agnostic: they either depend on an "attribute" property which is expected to be "shaped" like an Attribute object (which we want to avoid) or they call directly a method that makes attribute-related operations only.

Some components like ColorHue are perfectly instantiated in AttributeItemDelegate, with the slots correctly defined upon instantiation (rather than directly within the component) and this is what we should be doing with the other components as well. (there's just a minor hiccup regarding the direct reference to the "attribute" property, we should only declare and forward the value directly)

The ideal would be to have no mention whatsoever to attributes within the components, as is done in the Choice.qml and ChoiceMulti.qml files.

However the split between components is exactly what we expect (except maybe for the PushButton.qml which does really do anything beside instantiating a standard button) and this heavily improves the readability of AttributeItemDelegate.qml. Most of the hard work has already been done, so kudos on that part!