fix(hmr): After HMR app is blank when re-launched

[vakrilov]

PR Checklist

• The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• There is an issue for the bug/feature this PR is for. To avoid wasting your time, it's best to open a suggestion issue first and wait for approval before working on it.
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• Tests for the changes are included.

What is the current behavior?

Can be reproduced with the hello-word template on Android:

1. Create an app an run it
2. Make a change in item.service.ts to trigger HMR
3. Exit the app with the back button
4. Run the app again - it is blank

What is the new behavior?

The app is rendered as expected after re-launch.

The actual problem fixed is that the launchCallback was using an outdated instance of AppHostView instead of creating new host view on every launch.

[dtopuzov]

test --ignore