GH-3558: LiteralLabel lazy value

[afs]

GitHub issue resolved #3558

• Literal label lazy mode active
• Note changes to datetime to support years greater than 2 billion (jena-core)
• Tidy code in areas looked at while working on this PR

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• No test changes - this confirms lazy mode operation
• Commits have been squashed to remove intermediate development commit messages.
• Key commit messages start with the issue number (GH-xxxx)

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