feat: speed-up livesync with HMR

[rosen-vladimirov]

In case HMR is used, webpack reports to CLI the already prepared files, so there's no need for CLI to do any preparation, just sync the files. Try sending them as soon as possible and if we fail, go through the normal worklfow.

Ensure the code is called only when webpack had produced files for us and we are with HMR enabled.

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.
• You have signed the CLA.
• All existing tests are passing: https://github.com/NativeScript/nativescript-cli/blob/master/CONTRIBUTING.md#contribute-to-the-code-base
• Tests for the changes are included.

What is the current behavior?

Applying a change when CLI is livesyncing with HMR takes from 1.5 to 5 seconds.

What is the new behavior?

Applying a change when CLI is livesyncing with HMR takes from below 1 second.