Add the `components` package with PathMappingControl

[adamziel]

Motivation for the change, related issues

Adds a PathMappingControl React component:

The short-term goal is to eventually replace the current mapping control based on text inputs:

The long-term goal is to create a library of dependency-free components (well, aside of React) to reuse between Playground webapp, WordPress plugins, WordPress blocks, and the Blueprints builder. This path mapping widget will make a good fit for all these places.

Implementation details

The PathMappingControl uses WordPress components under the hood. Most notably, TreeGrid and Button. I considered using web components for portability, but decided against it because they:

• Wouldn't have the native WordPress look and feel
• Couldn't easily mix with WordPress components
• Had some issues around focus management

Testing Instructions (or ideally a Blueprint)

1. Run nx dev playground-components
2. Go to http://localhost:5173/
3. Play with the widget and confirm it works intuitively

Follow-up work

• Replace the text input under Absolute path in Playground with a UI-based picker or path autocompletion.
• Implement mapping validation to make sure there are no nested mappings, e.g. /wordpress/wp-content and /wordpress/wp-content/plugins.
• Reuse the base TreeGrid as a file browser in the Playground block (need asynchronous loading)

[adamziel]

I'll remove this from the board for now. We'll need it sooner than later but let's not occupy a space in a queue.

[adamziel]

UX idea: display select boxes for path selection, not inputs. Options:

• Plugin
• Theme
• Mu-plugin
• Uploads
• Wp-content
• WordPress root
• Custom path -> this one shows an input

In v2 we could also add a magic "guess" button to infer the role of every path in the tree.

[brandonpayton]

UX idea: display select boxes for path selection, not inputs. Options:

Nice. This would reduce the opportunity for typos, and selection sounds less stressful to me than having to remember and type the correct path.

[adamziel]

There are improvements we could do here, but I'll go ahead and merge as it's not used anywhere and I'd like to play with it in a draft branch.