InstructionsWithWorkspace owns the resizer

[islemaster]

LP-838: As a first step towards simplifying our instructions resize code, moves ownership of the HeightResizer component up out of TopInstructions into the InstructionsWithWorkspace component.

I believe this makes more sense - TopInstructions and CodeWorkspace are both rendered by InstructionsWithWorkspace, both respecting the instructions size currently stored in redux. At the moment, TopInstructions also owns the resizer control that sits between these two resizable areas, but it's unclear why TopInstructions should be concerned with this resize bar, rather than simply rendering in the space it's given. (There are circumstances where content changes inside the instructions will trigger a container resize, but that seems like a side-effect, not a primary concern).

In the new setup, TopInstructions, HeightResizer and CodeWorkspace are siblings, and their parent InstructionsWithWorkspace owns the resize logic that governs these three components.

This is nearly a pure refactor - from a behavior point of view everything should be exactly the same. The structure of the DOM changes a bit, with the resizer moving out a few layers.

Testing story

My approach to this change:

1. Pin existing resize behavior with an integration test on InstructionsWithWorkspace.
2. Move HeightResizer, keeping tests passing.
3. Do a little code cleanup to make things read nicely.

Also manual testing on CSF and non-CSF levels to sanity check that the resizer still looks and feels the same.

Reviewer Checklist:

• Tests provide adequate coverage
• Code is well-commented
• New features are translatable or updates will not break translations
• Relevant documentation has been added or updated
• User impact is well-understood and desirable
• Pull Request is labeled appropriately
• Follow-up work items (including potential tech debt) are tracked and linked

[dmcavoy]

LGTM. I like that this pulls HeightResizer out if TopInstructions.

I'm wondering if the next step after this is looking into the redux store which is managing instructions height and trying to simplify some of the complexity there.