chore: update build process to use ng-packgr builder

[wSedlacek]

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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• All existing tests are passing: https://github.com/NativeScript/angular/blob/master/DevelopmentWorkflow.md#running-the-tests
• Tests for the changes are included.

What is the current behavior?

The build process was previously using a custom script.

What is the new behavior?

With advancements in the ng-packgr the custom build script is no longer necessary and all processes it was doing can be left to the ng-packgr executor.
With using the executor it makes the build no longer include the es2015 bundles which were removed from the recommended Angular Package Format with the release of Angular 13