fix: restore getEntryPathRegExp for backward compatibility with older…

[KristianDD]

… webpack.config.js

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?

If the user doesn't update webpack.config.js, build fails.

What is the new behavior?

If the user doesn't update webpack.config.js, build succeeds.

Fixes/Implements/Closes #[Issue Number].

[KristianDD]

test branch_ngapps#release ngapps#release