[docs] Updates in Expo Modules guides

[tsapeta]

Why

Further improvements on the Expo Modules docs page

How

• Took Expo Modules API out of Alpha.
• Renamed Expo Modules API to just Expo Modules (sidebar on the left). This is actually not a single API, but a set of APIs + the shorter name is always better.
• Renamed Module API to Native Modules, I think this will be more clear for people.
• Added more examples of packages using the new API for native modules.
• Moved ViewManager component to be before View and Props (you use ViewManager first in your module definition, so this seems to be a more natural order).
• Clarified that view managers are still experimental and we're working on integrating it with Fabric. Also noted that we plan to support SwiftUI but until then people can embed SwiftUI views using UIHostingController.
• Added missing description to OnActivityEntersForeground, and OnActivityEntersBackground components.
• Added Primitives section to Argument Types to make it clear what primitive types are supported as arguments.
• Changed naming convention a little bit: Expo module API -> Expo Modules API for native modules or Expo native modules API. Again, this is to clarify it's about the native module. iOS AppDelegate subscribers and Android lifecycle handlers are also Expo module APIs, but they are not the same as native modules.

Test Plan

Looks good locally

[kbrandwijk]

There's 'Expo native modules API', 'Expo Modules API for native modules', 'Expo Modules', 'Expo Modules API', was there any verdict on final verbiage yet?