[Feature] Add Alert When Network Lost

[jpeng-ms]

Purpose

The goal is to alert Contoso user they cannot join the call if their internet is down.

Technical details

This PR introduces a network manager which listens to system event on network condition.
Setupviewmodel would be responsible to dispatch error actions to update network state, which would be used by error banner view accordingly.

The overall flow is the following:

in the event of network lost:

nothing would happen until user tap on "join call" button:

1. setup view model would ask manager if network is online

2. if network is down, dispatch an error action with type .connectionFailed

3. then it would be handled by error reducer

4. error state would be updated

5. error banner view model which listens to error state changes would then display error without any involvement of set up view model or network manager.

Does this introduce a breaking change?

[ ] Yes
[X] No

Pull Request Type

What kind of change does this Pull Request introduce?

[ ] Bugfix
[X] Feature
[ ] Code style update (formatting, local variables)
[ ] Refactoring (no functional changes, no api changes)
[ ] Documentation content changes
[ ] Other... Please describe:

How to Test

1. clone the repo
2. set target to demo app
3. select a physical device
4. click run

What to Check

1. when there's no active internet connection, an alert should be shown when you tap on "Join Call"

Other Information

1. The scope of this ticket is limited to set up view only and we should not handle anything on calling view as it's calling SDK's task to let us know about call conditions.
2. Please use physical device for testing. The network changes on your laptop does not propagate to simulator properly and you might notice unexpected behaviour due to this. 3.

Expected Behaviour

1. launch composite + network down = no error banner
2. tap on "join call" + network down = error banner shown
3. dismiss error banner + tap on "join call" + network down = new error banner shown
4. error banner shown + tap on "join call" + network down = no action
5. error banner shown + tap on "join call" + network back online = error banner remains then gets dismissed when join call button changes to "joining the call..." with a loading spinner.
6. error banner shown + state changes (change audio/speaker/camera, enter background/foreground, swipe down notification, etc.) = error banner remains no action
7. dismiss error banner + state changes = no action, error banner stays hidden
8. SDK error + network down = error banner would take SDK error unless user taps on "join call" then SDK error would be replaced to network offline.

Screenshots

SDK error when network is offline (without tapping on join call):

SDK error when network is offline (after tapping on join call):

UI:

[kevinyulu]

tested on device LGTM