Add a way to clear only static cache

Problem/Motivation

Currently the only option to reset an individual controller's static cache is to invoke the ::resetCache() method. Unfortunately this also triggers a clear of the persistent cache, which is wasteful and in some edge cases (e.g. while dumping a database) may lead to errors, due to tables being truncated, which is not a transactional-safe operation.

A workaround for this is invoking drupal_static_reset(), which clears entity_get_controller()'s static cache, leading to new controllers being instantiated. However, if there are lingering references to the old controller instances, those will still have a stale entity cache, which may lead to inconsistent behaviors and crazy to debug™ scenarios.

Proposed resolution

Add a new EntityCacheEntityControllerInterface for entity cache-aware controllers exposing a ::resetStaticCache() method.

Remaining tasks

• Validate the prosed solution
• Post a patch
• Reviews

User interface changes

None

API changes

Only additions

Data model changes

None

Release notes snippet

A new method is available for entity cache-aware controllers to reset only static cache.