Transformations: Add context to transformation editor

[mdvictor]

What is this feature?

Adds context inside the transformation editor. This makes sure that a field calculation transformation which uses variables does get its variables interpolated and doesn't return undefined (and thus does creates a new field that is visible for other transforms further in the pipeline, e.g: organise).

Why do we need this feature?

Fix a bug where new fields created through field calc using variables where not visible in the final dataframe in the editor.

Who is this feature for?

Everyone

Which issue(s) does this PR fix?:

Fixes #76090

Special notes for your reviewer:

Please check that:

• It works as expected from a user's perspective.
• If this is a pre-GA feature, it is behind a feature toggle.
• The docs are updated, and if this is a notable improvement, it's added to our What's New doc.

[oscarkilhed]

🎉