Assign inter-feature dependencies

Problem/Motivation

Currently there is no handling of dependencies between features.

Proposed resolution

• Analyze package configuration and introduce inter-feature dependencies based on configuration dependencies. Example: if feature A provides a content type required by a field instance in feature B, feature B has a dependency on feature A.
• Only assign dependencies on features that are either (a) already exported and enabled on the site or (b) part of a set of features being generated.

Remaining tasks

These should be either dropped or moved to follow-up issues.

• Dependency management will need to include removing superfluous dependencies. E.g. if both feature A and feature B have a dependency on the 'example' feature and we introduce a new dependency of feature B on feature A, feature B no longer needs an explicit dependency on the 'example' module.
• To maintain interoperability, special handling may be needed for the 'core' package. That is, many features will have a dependency on the 'core' package, e.g., for providing field definitions. However, we should avoid introducing a dependency on that particular feature, since doing so would prevent combining features from multiple feature sets. Proposed resolution: skip the 'core' module when assigning dependencies and instead make 'core' a dependency of the install profile, if one is created. See also #2447703: Integrate with Configuration Share and Compatible.

User interface changes

API changes