Event: Filter Drupal core branch/release component after project selection

[nerdstein]

The advanced option selection of a Drupal core version should be filtered based on the branch/release of the initial project branch selected.

Example: If someone selected Password Policy and version 8.x-3.x, this should...

1. Make the Drupal core selection visible.
2. Populate the Drupal core selection list with only 8.x or 7.x releases (filter by major release)