Further speed-ups in ConfigurableResourceType::getResourceFieldConfiguration()

Problem/Motivation

We've added a static cache layer in #3007091: Performance issue in ConfigurableResourceType, but we are misusing it a bit :)...

Internally the static cache implementations are checking:

// ...
if (!isset($cache->data)) {
  return FALSE;
}
// ...

So when we save NULL this is essentially cache misses on the next cache get for the item.

Before:

After:

Proposed resolution

My proposal is to use FALSE as a tombstone in the cache and have a single ternary operation to fix the return value to a NULL as the interface is promising.

Patch will follow soon.

Remaining tasks

Patch discussion commit.

User interface changes

None.

API changes

None.

Data model changes

None.

Release notes snippet

None.