[hibernate-dev] Minor SPI *addition*

I don't think this should require a new CR as it is an *addition* to an SPI, but wanted to run it past everyone and get y'alls thoughts. I ran across the need for this while re-working the documentation. Basically I needed a (easy) way to allow users to override the implicit resolution for a built-in basic type. So I added the following method to MetadataBuilder: applyBasicType(BasicType type, String... keys) specifically passing in some keys, intending to allow overriding the keys defined by BasicType. To that end I did have to make one additional change to add a new type, BasicTypeRegistration, to act as a tuple for the BasicType+keys and MetadataBuildingOptions#getBasicTypeRegistrations to return this type rather than "just" returning BasicType. The specific use-case was to allow users to easy remap how UUID attributes are handled (store as CHAR rather than BINARY). But really it is useful for altering any implicit attribute type mapping.