WIP: Implement client side rendering

[johnbillion]

This starts us down the path of switching over Query Monitor's output to client-side rendered React components.

This has numerous benefits including:

• Better performance (no need to render a big pile of HTML)
• Allowing for state to be swapped out in order to show data for requests other than the current page load (eg. Ajax, REST API, POSTs before a redirect, and historical requests)
• Panels which can be reused outside of the context of WordPress, eg in loggers or browser extensions
• Data accessible elsewhere in the client, eg in the developer tools panel

There's still lots to do, but the concept has been proven.

See #291.

Progress

• [x] Proof of concept
• [x] Functional
• [ ] Quality
• [ ] Functionally complete
• [ ] Shiny and ready to go

Aims

• Feature parity with all existing panels.
• JSON data payload to hydrate the client-side panels. Remove unnecessary properties as we go.
• Retain support for server-side rendered panels so add-ons for QM and Debug Bar continue to work.
• ~~Partial client-side rendering. The main panel container and its menu tabs will remain server-side rendered for the time being. Individual panel contents will be converted to client-side rendering.~~
• Retain and continuously improve the existing server-side panel rendering until all client-side panels are complete.
• Publish the UI components as an NPM package
• Remove dependency on jQuery

Considerations

• Bundling for WP backwards compatibility. wp.i18n isn't bundled with WP prior to 5.0.
• Bundling in general. Should React be bundled or should core's be used?
• Using data across components, eg most stuff in the Overview panel
  • Slot & Fill?

Usage

npm install --legacy-peer-deps && npm run watch

Per-panel Tasks

The existing collectors and outputters in QM are very well separated, but nevertheless as each panel is worked on the following actions may need to be made:

• Move logic out of the HTML outputter and into the corresponding collector.
• Move translatable strings out of the collector and into the corresponding HTML outputter and React component.

Panel Progress

• [ ] overview
  • Use a slot that other components can fill with their data
• [x] admin
• [x] assets_scripts
• [x] assets_styles
• [x] block_editor
• [ ] cache
• [x] caps
• [x] conditionals
• [x] db_callers
• [x] db_components
• [x] db_dupes
• [x] db_queries
• [x] environment
• [ ] headers
• [x] hooks
• [x] http
• [x] languages
• [x] logger
• [x] php_errors
• [ ] raw_request
• [x] request
• [x] theme
• [x] timing
• [x] transients
• [ ] Hooks in Use panels
• [x] Settings panel

UI Component Progress

• [x] Toggles
• [ ] Filter dropdowns
• [ ] Filter links
• [ ] Table sorters
• [ ] Clickable stack traces
• [x] Table footers

Nope

The following panels will remain server-side rendered:

• [x] debug_bar