Add a `ConfigurationPropertyCaching` utility interface that can be
used to control the property source caching.
Prior to this commit, a `ConfigurationPropertySource` that was backed
by a mutable `EnumerablePropertySource` would need to call the
`getPropertyNames()` method each time a property was accessed. Since
this this operation can be expensive, we now provide a way to cache
the results for a specific length of time.
This commit also improves the performance of immutable property sources
by limiting the number of candidates that need to be searched.
Previously, all mapped names would be enumerated. Now, mappings are
grouped by `ConfigurationPropertyName`. This is especially helpful when
the `ConfigurationPropertyName` isn't mapped at all since the hash based
map lookup will be very fast and the resulting mappings will be empty.
Closes gh-20625
7afd25fc9a