Related to #72317 with the final goal of bringing global styles to the post editor.

What?

Refactors the styles canvas state management and rendering architecture in the Site Editor to simplify the codebase. This is a preparation to moving the stylebook and the style-canvas to the editor package (to be used in edit-post too)

Why?

The previous EditorCanvasContainerView implementation had several issues:

1. Complex string-based state: Used composite strings like 'global-styles-revisions:style-book' that were difficult to understand and maintain
2. Bidirectional state sync: The canvas-link.js file attempted to keep canvas overlay state in sync with navigation state, requiring complex usePrevious() hooks to prevent infinite loops
3. Scattered responsibility: Rendering logic was distributed across multiple files making it hard to understand when/how overlays render
4. Architectural issues: Double wrapping with EditorCanvasContainer, redundant effects, and unclear component hierarchy

How?

State Management

• Replaced string-based editorCanvasContainerView with structured state: stylesNavigation: { path, showStylebook }
• Created orthogonal concerns: path for navigation, showStylebook for presentation mode
• Redux as single source of truth - eliminated bidirectional sync complexity

Component Architecture

• Created centralized StylesCanvas orchestrator that decides what canvas to render based on Redux state
• Co-located related files in styles-canvas/ folder:

Testing Instructions

1. Open the Site Editor and navigate to Styles
2. Test StyleBook toggling:
   • Click the "Style Book" toggle button to open the stylebook overlay
   • Verify the overlay fills the full height
   • Click the close button (X) in the overlay
   • Click "Style Book" again - verify it reopens correctly
   • Repeat this open/close cycle 3-4 times to ensure no state bugs
3. Test Revisions:
   • In the Styles sidebar, click the "Revisions" button (if available)
   • Verify the revisions overlay appears
   • Close it and verify you can reopen it
4. Test navigation cleanup:
   - Open the stylebook
   - Navigate to a different screen (Templates, Pages, Patterns)
   - Verify the stylebook overlay closes automatically
   - Navigate back to Styles
   - Verify you can open stylebook again
5. Test in editor context:
   - Open a post or page in the editor
   - Open the Styles panel from the sidebar
   - Toggle the stylebook - verify it works correctly
   - Close and reopen multiple times