Move `PropertyPath` and `TypeInformation` types to `core` package

[mp911de]

To improve our design in preparation for evolution of the Spring Data design, we should introduce a core package and move the following types into these:

org.springframework.data.mapping -> org.springframework.data.core

Affected types:

• PropertyPath
• PropertyReferenceException

org.springframework.data.util -> org.springframework.data.core

Affected types:

• CustomCollections and CustomCollectionRegistrar
• NullableWrapper
• NullableWrapperConverters
• ReactiveWrappers
• TypeInformation

The motivation is to leverage property paths on the domain type level reflecting their actual conceptual usage of property paths. For example, Sort and ExampleMatcher were designed to use property paths which is a conceptual cycle pointing into the mapping package.

By moving PropertyPath support and related types (TypeInformation, wrapper and collection infrastructure) into a newly created core package we're resolving the design cycles resulting in an improved design reflecting the actual intended dependencies.