In case CLI is used as a library and isValidNativeScriptProject is called multiple times, it does not return correct results after the first time.
The problem is that it uses the singleton object - projectData. Change the implementation to use projectDataService, this way the method will always return correc results.

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?

In case CLI is used as a library and isValidNativeScriptProject is called multiple times, it does not return correct results after the first time.

What is the new behavior?

In case CLI is used as a library and isValidNativeScriptProject is called multiple times, it returns correct results.