[61] Re-introduce block editor visual preview

[g-elwell]

Description

This PR re-introduces the visual block editor preview that was previously included before we switched to a code view for MVP. The preview can now be toggled between visual and code modes, and the visual mode can be set to display either a predefined block preview, or individual blocks based on the currently selected navigation item.

Fixes #61

Change Log

• Bumps the minimum WordPress version to 6.4, required for the block editor preview
• Adds a block editor for previewing style changes visually
• Adds a toggle to switch between visual and code previews
• Adds a size selector to toggle between desktop/tablet/mobile widths for the visual preview
• Adds a 'follow' button to enable the visual preview to render block/element previews based on the navigation
• Minor refactoring and tidying of code

Steps to test

• Install the plugin, navigate to Appearance > Styles Editor
• Check the visual preview reflects style changes
• Toggle the 'preview mode' to switch between code/visual previews
• Toggle the 'preview size' to switch between desktop/tablet/mobile widths
• Turn on the preview 'follow' button (eye symbol) and check the visual preview will render the correct block/element based on the selected item in the navigation

Screenshots/Videos

Screen.Capture.on.2024-10-01.at.21-31-46.1.mp4

Checklist:

• My code follows the style guidelines of this project
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• My changes generate no new warnings
• Any dependent changes have been merged and published in downstream modules