fix: native frameworks/code is added to tns_modules dir

[rosen-vladimirov]

The <project dir>/platforms/<platform>/.../tns_modules directory should contain only the .js code of the application. However, in case nativescript plugin is installed in the node_modules directory of another package (not directly inside the project), its platforms directory is copied to tns_modules as well. This leads to error when trying to build application that has such structure with Xcode 10.
After copying the node_modules to tns_modules recursively remove all platforms directories of all nativescript plugins inside node_modules.

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. - QAs will add test for this case

What is the current behavior?

Build with Xcode fails when nativescript plugin is installed as dependency in node_modules (i.e. it is not installed directly in the node_modules dir of the project.

What is the new behavior?

Build succeeds

Fixes #3932