Extracted SPI build for DATAJPA-564 into Spring Data Commons. Simplified the configuration setup code and removed the ability to define a custom EvaluationContextProvider for now. We directly declare a bean definition which automatically picks up EvaluationContextExtensions.
RepositoryFactory(Bean)Support is now aware of the EvaluationContextProvider to hand it to the template method that creates the QueryLookupStrategy. Deprecated the previously existing template method in favor of an extended one.
Removed variable declarations from the extension interface for now as usually properties serve the same purposes as variables which makes the latter superfluous for now. Applied some JavaDoc and API signature polish. Added unit tests for ExtensionAwareEvaluationContextProvider.
Related pull request: spring-projects/spring-data-jpa#101
Related ticket: DATAJPA-564
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