Add a general purpose `Configurations` class that encapsulates the
sorting and merging rules that are usually apply. The class is
particularly useful in tests where configuration classes often need
to be specified, but an `@Import` or `ImportSelector` cannot be easily
used.
Two `Configurations` subclasses have been initially added. The
`UserConfigurations` class can be used to represent user defined
configuration and the `AutoConfigurations` class can be used to
represent a subset of auto-configurations. Auto configurations are
sorted using the same `@AutoConfiguraionBefore`/`@AutoConfiguraionAfter`
logic as the `@EnableAutoConfiguration` annotation.
Fixes gh-9795
2f0f25f5ad