Replace WPAuthenticator UI code in ChangeUsernameViewController.swift

[crazytonyli]

Note

I recommend reviewing this PR commit by commit. The first commit is format-only.

Description

Part of removing WordPressAuthenticator. Some UI elements from WordPressAuthenticator are used in the app, which we don't need to.

Before	After

Testing instructions

• Me -> Account Settings -> Username: search suggestions, selection checkmark, and Save enablement.
• The domain registration details form (register a domain with a paid plan) for the InlineEditableNameValueCell rows.

[dangermattic]

	1 Warning
⚠️	This PR is larger than 500 lines of changes. Please consider splitting it into smaller PRs for easier and faster reviews.

Generated by 🚫 Danger

[wpmobilebot]

📲 You can test the changes from this Pull Request in WordPress by scanning the QR code below to install the corresponding build.

	App Name	WordPress
	Configuration	Release-Alpha
	Build Number	32577
	Version	PR #25647
	Bundle ID	org.wordpress.alpha
	Commit	755d905
	Installation URL	7tpdifgpasuig

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.

[wpmobilebot]

📲 You can test the changes from this Pull Request in Jetpack by scanning the QR code below to install the corresponding build.

	App Name	Jetpack
	Configuration	Release-Alpha
	Build Number	32577
	Version	PR #25647
	Bundle ID	com.jetpack.alpha
	Commit	755d905
	Installation URL	0esjlvcndf8qo

Automatticians: You can use our internal self-serve MC tool to give yourself access to those builds if needed.