Improve TSDocs for Core services

[joshdover]

All services exposed via the public and server PluginInitializerContext, CoreSetup, and CoreStart need to have comprehensive TSDocs in order to make our generated markdown docs useful.

At a minimum, each top-level service should include:

1. What the services is responsible for and what situations should it be used in.
2. Examples of how to use the different methods of the service together.
3. Descriptions on each function or value exposed by the service that explains what it does.

/**
 * ChromeStart allows plugins to customize the global chrome header UI and
 * enrich the UX with additional information about the current location of the
 * browser.
 *
 * @remarks
 * While ChromeStart exposes many APIs, they should be used sparingly and the
 * developer should understand how they affect other plugins and applications.
 *
 * @example
 * How to add a recently accessed item to the sidebar:
 * ```ts
 * core.chrome.recentlyAccessed.add('/app/map/1234', 'Map 1234', '1234');
 * ```
 *
 * @example
 * How to set the help dropdown extension:
 * ```tsx
 * core.chrome.setHelpExtension(elem => {
 *   ReactDOM.render(<MyHelpComponent />, elem);
 *   return () => ReactDOM.unmountComponentAtNode(elem);
 * });
 * ```
 *
 * @public
 */

Services that need improvement

Public APIs

• HttpSetup
• NotificationsSetup
• UiSettingsSetup
• ApplicationStart (@joshdover)
• ChromeStart (@joshdover)
• DocLinksStart
• HttpStart
• I18nStart - this service needs to change, probably not worth doing now
• OverlaysStart
• UISettingsStart

Server APIs

• CoreSetup.elasticsearch
• CoreSetup.http
• SavedObjects
  • How references work / what they do

[elasticmachine]

Pinging @elastic/kibana-platform

[joshdover]

I'll be doing an audit here and creating issues for any services that still need additional docs.

[joshdover]

Fixed by #47069