feat(external_api) exposes more events from JS to native and adds the ability to send actions from native to JS.

Android < 23 is currently less than 3% for us so let's try to lower the
maintenance burden. Users can still download an older version no problem.

When exiting PiP with by pressing the X the onPictureInPictureModeChanged method
is called. Since onResume is called a while after, in case the maximize button
is called, it's not easy to know if the user pressed the X button, and that was
the cause for exiting PiP.

So, in order to avoid show the user they are still in the meeting, bring the
activity to the foregound so they can hangup.

Android for Enterprise provides special feature for applications to obtain configuration through RestrictionManager remotely by some MDM solution.

Jitsi Meet can be remotely installed and provisioned with a proper URL (making URL not editable by the user) inside the Work Profile or Fully managed device.

It's the source of uncountable problems for which we don't have a good
solution, since they are caused by buggy implementations of self-managed
connection services by manufacturers.

The notification is posted by a foreground service, which also has the nice
side-effect of keeping the app alive for a long time.

It may be called in the Activity instead of in the Fragment. Handle both.

At the moment it includes:

- display name
- email
- avatar URL

This information is used *only* if no token was specified.

A libre build will exclude the following:

- Analytics modules
- Google Play services GMS
- Crashlytics
- Firebase

Consolidate all failure cases into a single one: CONFERENCE_TERMINATED. If the
conference ended gracefully no error indicator will be present, otherwise there
will be.

It renders a single JitsiMeetFragment which holds the JitsiMeetView view.

Co-authored-by: Saúl Ibarra Corretgé <saghul@jitsi.org>

Add JitsiMeetFragment and refactor the app to use it.

We are going to implement the invite dialog *inside* the SDK, so there is no
need to have all this machinery anymore.

These values must match these ones in React Native:
5939d078a0/ReactAndroid/src/main/java/com/facebook/react/modules/systeminfo/AndroidInfoHelpers.java (L20-L22)

This is done at the app level, not the SDK.

Currently 2 Firebase services are used:

  - Crashlytics
  - Dynamic Links

They are enabled in tandem, if the appropriate Google services file
(GoogleService-Info.plist on iOS or google-services.json on Android) is found.

Each service needs to be individually enabled in the Firebase console.

Note that Android 9 Pie (API 28) disallows HTTP requests by default, so an
exception was needed in the app in order for the Metro bundler to work in debug
mode.

Glide (which is used by react-native-fast-image) can cause trouble if the host
app (the one using the SDK) is using Glide already.

To avoid this, don't use the builtin AppGlideModule (as the docs recommend) and
let apps define it.

Since this is a feature implemented in the SDK, it makes sense that all the
plumbing required to make it work it's in the SDK itself.

LeakCanary is a memory leak detection library which will run only in Debug mode.

* Button conditionally shown based on if the feature is enabled and available
* Hooks for launching the invite UI (delegates to the native layer)
* Hooks for using the search and dial out checks from the native layer (calls back into JS)
* Hooks for handling sending invites and passing any failures back to the native layer
* Android and iOS handling for those hooks

Author: Ryan Peck <rpeck@atlassian.com>
Author: Eric Brynsvold <ebrynsvold@atlassian.com>

This only works automatically on Android >= 8. On other platforms / versions, it
relies on the SDK user on implementing a "reduced UI" mode and reacting to the
"request PIP" delegate method.

* Javadoc introduced @code as a replacement of <code> and <tt> which is
  better aligned with other javadoc tags such as @link. Use it in the
  Java source code. If we switch to Kotlin, then we'll definitely use
  Markdown.

* There are more uses of @code in the JavaScript source code than <tt>
  so use @code for the sake of consistency. Eventually, I'd rather we
  switch to Markdown because it's easier on my eyes.

* Xcode is plain confused by @code and @link. The Internet says that
  Xcode supports the backquote character to denote the beginning and end
  of a string of characters which should be formatted for display as
  code but it doesn't work for me. <tt> is not rendered at all. So use
  the backquote which is rendered itself. Hopefully, if we switch to
  Markdown, then it'll be common between JavaScript and Objective-C
  source code.

JitsiMeetViewListener is an integral part of the public API of Jitsi
Meet SDK for Android. Utilize it in the Debug configuration of the Jitsi
Meet app for Android in order to increase (1) awareness of API breakages
and (2) API coverage.

The same goes for JitsiMeetViewDelegate in Jitsi Meet SDK and app for
iOS.