Rename SQLRaw to SQLUnsafeRaw and SQLRawBuilder to SQLUnsafeRawBuilder

We really want to emphasize as much as possible that using raw SQL is unsafe. These changes also match up with the same renames in the Fluent 5 version of SQLKit. The original `SQLRaw` and `SQLRawBuilder` names are preserved as a deprecated `typealias`, as is the original `SQLDatabase.raw(_:)` spelling of what is now the `SQLDatabase.unsafeRaw(_:)` method.