fix: fix "ERROR in Must have a source file to refactor." error from ngCompilerPlugin on test command

[Fatme]

The "ERROR in Must have a source file to refactor." error is thrown when tns test android --path <projectPath> --bundle command is executed.
This error is thrown from AngularCompilerPlugin when the path to main.ts file is not correct. We provided the path to main.ts file here. As this path is built using path.resolve and appPath is relative path, the resulting path is still not an absolute path. In this case NodeJS uses current working directory as described here. In other words, in this case resolve(appPath, entryModule) is equal to join(process.cwd(), appPath, entryModule).

NativeScript CLI starts 2 webpack processes on test command - one from nativescript-dev-webpack plugin and another one from karma-webpack plugin.
When the webpack process is started from nativescript-dev-webpack plugin, cwd is explicitly set here. So, the result from resolve(appPath, entryModule) is correct and AngularCompilerPlugin is happy.
When the webpack process is started from karma-webpack plugin, cwd is not set anywhere, so the default value is used. It is fine and works as expected when test command is executed from project directory regardless if --path option is provided. It is not fine and the error is thrown in following cases:

• When test command is executed with --path option from folder different from project directory
• When test command is executed from CI where cwd is explicitly provided

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].

[dtopuzov]

test package_version#latest branch#release