feat: support @nativescript scope in host resover

[vakrilov]

PR Checklist

• [x] 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.
• [x] You have signed the [CLA].
• [x] All existing tests are passing: https://github.com/NativeScript/nativescript-dev-webpack/blob/master/CONTRIBUTING.md#testing-locally-by-running-e2e-tests
• [ ] Tests for the changes are included.

What is the current behavior?

Nativescript host resolver (used in angular projects) does not recognize package in @nativescript scope as "nativescript" packages and so does not resolve platform-specific files in there.

What is the new behavior?

"@nativescript" added in host resolver's list of nativescript packages.