People: Update name value for Jetpack/Atomic sites to point to most up to date source

[sixhours]

Changes proposed in this Pull Request

• Jetpack/Atomic sites sync data to WP.com mirror sites, but after the initial sync, not all data gets sent.
• Jetpack Sync only checks for changes in the user ID and capabilities after the initial sync; if a site gets disconnected, the rest of the user data does not get updated on reconnection/resync.
• This means you can end up in a situation where the People page on a Jetpack/Atomic site displays an old, out of date display name for a user, if the user updated their display name on WP.com while their Jetpack/Atomic site was disconnected.
• ...but we can access the most up-to-date name value via the API in a linked_user_info object that comes directly from WP.com's user info rather than the site's, so pointing to that value on the front end for Jetpack/Atomic sites shows the correct name, even if the synced site data is incorrect. If there's a mismatch, the user doesn't need to know about it.
• This is not a fix for the syncing problem, but a stopgap for showing the most up-to-date user info on the front end.

Fixes #55175

Before

Red lines indicate the old, incorrect display name, name we want to display indicated by a green arrow:

After

Green lines indicate the correct display name is now shown:

Testing instructions

• Spin up an Atomic test site
• Note your current Display Name under /me and visit your test site's people admin: /people/team/[site] -- you'll see your Display Name listed as a user
• Disconnect the Atomic test site from Jetpack via CLI: wp jetpack disconnect blog
• Update your Display Name under /me to something new
• Go back to /people/team/[site] and you'll see the old Display Name value
• Reconnect your site to Jetpack from /wp-admin -- the old Display Name value will persist at /people/team/[site]
• Switch to this PR and view /people/team/[site]; you'll see the correct, updated Display Name.

[github-actions]

Link to Calypso live: https://calypso.live?image=registry.a8c.com/calypso/app:commit-42f4102ed31db57fa07f8c089eee680f19a6a446
Link to Jetpack Cloud live: https://calypso.live?image=registry.a8c.com/calypso/app:commit-42f4102ed31db57fa07f8c089eee680f19a6a446&env=jetpack
(These links may take a few minutes to be available)

[matticbot]

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

Sections (~13 bytes added 📈 [gzipped])

name    parsed_size           gzip_size
people        +46 B  (+0.0%)      +13 B  (+0.0%)

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

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.

[sixhours]

Ahh darn, I just realized this doesn't solve the problem, really. Because there are more places (ie. /posts) where the incorrect username will still be displayed. Unless we catch all instances of the Display name across Calypso, a front-end approach probably won't work. I'll keep investigating the backend approach.