Mulgara

This is the next cleanup refactoring.
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We have:
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[[ResolverFactory]] findModelResolverFactory(long model)
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[[ResolverFactory]] findUncachedExternalResolverFactory(long model)
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[[ResolverFactory]] findModelTypeResolverFactory(URI modelTypeURI)
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Resolver obtainResolver(ResolverFactory resolverFactory)
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URI mapToModelTypeURI(URI modelURL)
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URI findModelTypeURI(long model)
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String findProtocol(long n)
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most of which do multiple overlapping tasks, often implemented slightly differently.
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Most of these methods used to live in different classes, and have migrated here as their homes were refactored and tidied.
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[[DatabaseOperationContext]] and [[LocalQueryResolver]] are the last two dumping grounds in the system-core where we have left the cruft that was too difficult to clean up concurrently with previous refactorings; and [[DatabaseOperationContext]] is by far the worst of the two - so it's next on the list.