Upstreaming Quantizer tool (part 2).

Upstreaming Quantizer tool (part 2).

    This adds some additional core types and utilities, notably the constraint analysis graph (CAG) structures, associated metadata and configuration policy object base class.

    The CAG is not particularly memory efficient as it stands now. I had started some work to turn it into a form that could be better managed by a bump pointer allocator but abandoned that for now in favor of having something that does semantically what I was going for as a starting point.

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PiperOrigin-RevId: 248413133