Search: Add "search"/"done" button to keyboard when searching (for a site address, domain, username)

Expected behavior

When there's a search feature in the app, I expect an obvious Search or Done button to appear on the keyboard, to make it clear that I have to tap it to complete the search. Here's an example from Reader > Search:

Actual behavior

In some searches, there isn't any button like that:

• Create a WordPress.com site: search for the site address
• Register a custom domain: search for the domain
• Create a WordPress.com account: search for a new username

In these cases, I often expect the app to update the search results as I type, and sit for a moment after entering my search before I realize I need to tap the "Enter" button on the keyboard:

Tested on iPhone XS, iOS 12.1, WPiOS 11.3.0.20181119

Start by locating the search input implementations for site-address creation, custom-domain registration, and username creation in the WordPress-iOS app. Compare their keyboard behavior with Reader > Search. Done means each listed search shows an obvious Search or Done keyboard button and the button completes the search as expected on iOS.