fix: exclude files from tests folder from built application

[Fatme]

Currently unit tests files and their dependencies are always included in the built application regardless if tns test or another command is executed. This way the size of built package is increased as all unit test related dependencies are included (such as mocha, chai, angularTestBed and their dependencies as well).

Rel to https://github.com/NativeScript/nativescript-dev-webpack/issues/1041

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-dev-webpack/blob/master/CONTRIBUTING.md#testing-locally-by-running-e2e-tests
• [ ] Tests for the changes are included.

What is the current behavior?

What is the new behavior?

Fixes/Implements/Closes #[Issue Number].