Reader Onboarding: Implement preview pane and selectable sites

[DustyReagan]

Related to https://github.com/Automattic/loop/issues/188

Proposed Changes

• This PR introduces the preview panel and "highlighted" selectable sites for "step 2"
• It adds onItemClick and isSelected props to the ConnectedReaderSubscriptionListItem and ReaderSubscriptionListItem components.

Note

This PR does NOT implement a "completed" state when you click the "Continue" button. We'll handle that in a followup PR. It also does NOT implement the "Load more recommendations" feature, but the copy is left in to keep the translations warm.

Before	After

Why are these changes being made?

• Push Reader Onboarding forward.

Testing Instructions

• Use Calypso Live
• Go to /read?flags=reader/onboarding
• Ensure you are following 3 or more tags to unlock the "Discover and subscribe to sites you'll love" button.
• Click "Discover and subscribe to sites you'll love" to view the suggested sites.
• Click on some suggested sites to see them load in the preview pane.
• Check for regressions by going to /discover and interact with the sites listed under "Popular sites"
• Click on all the links and subscribe button in some of the sites under "Popular sites" and ensure they still work as expected.

Pre-merge Checklist

• Has the general commit checklist been followed? (PCYsg-hS-p2)
• Have you written new tests for your changes?
• Have you tested the feature in Simple (P9HQHe-k8-p2), Atomic (P9HQHe-jW-p2), and self-hosted Jetpack sites (PCYsg-g6b-p2)?
• Have you checked for TypeScript, React or other console errors?
• Have you used memoizing on expensive computations? More info in Memoizing with create-selector and Using memoizing selectors and Our Approach to Data
• Have we added the "[Status] String Freeze" label as soon as any new strings were ready for translation (p4TIVU-5Jq-p2)?
• For changes affecting Jetpack: Have we added the "[Status] Needs Privacy Updates" label if this pull request changes what data or activity we track or use (p4TIVU-aUh-p2)?

[github-actions]

Calypso Live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-122235

Jetpack Cloud live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-122235&env=jetpack

Automattic for Agencies live (direct link)

https://calypso.live?image=registry.a8c.com/calypso/app:build-122235&env=a8c-for-agencies

[matticbot]

Here is how your PR affects size of JS and CSS bundles shipped to the user's browser:

Sections (~330 bytes added 📈 [gzipped])

name    parsed_size           gzip_size
reader       +938 B  (+0.1%)     +330 B  (+0.1%)

Sections contain code specific for a given set of routes. Is downloaded and parsed only when a particular route is navigated to.

Async-loaded Components (~88 bytes added 📈 [gzipped])

name                      parsed_size           gzip_size
async-load-design-blocks       +217 B  (+0.0%)      +88 B  (+0.0%)

React components that are loaded lazily, when a certain part of UI is displayed for the first time.

Legend

What is parsed and gzip size?

Parsed Size: Uncompressed size of the JS and CSS files. This much code needs to be parsed and stored in memory.
Gzip Size: Compressed size of the JS and CSS files. This much data needs to be downloaded over network.

Generated by performance advisor bot at iscalypsofastyet.com.

[matticbot]

This PR modifies the release build for the following Calypso Apps:

For info about this notification, see here: PCYsg-OT6-p2

• notifications
• wpcom-block-editor

To test WordPress.com changes, run install-plugin.sh $pluginSlug try/reader-onboarding-preview on your sandbox.

[davemart-in]

Progress looks great!