fix: allow overriding the `global.process` object

[DimitarTachev]

By default global.process will be undefined but the plugins and the app developers will be able to polyfill it. This will unify the behavior with the Legacy Workflow.

PR Checklist

• [x] The PR title follows our guidelines: https://github.com/NativeScript/NativeScript/blob/master/CONTRIBUTING.md#commit-messages.
• [x] 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.
• [x] You have signed the [CLA].
• [x] 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.

Related to: https://github.com/NativeScript/nativescript-dev-webpack/issues/921

[DimitarTachev]

test package_version#rc