[Tracking Issue] Collage Partitioner

[mbaret]

This is a tracking issue for the Collage partitioner which is described in RFC 62.

Links to the pull requests will be added to the following items as they are upstreamed.

• Introduce the partitioning infrastructure with basic PartitionRules.
• Add further more complex PartitionRules.
• Introduce CostEstimators to estimate the cost of partitions.
• Introduce the CollagePartition pass which generates and estimates the cost of many different partitioning options and searches for the optimal partitioning using a Dijkstra-style algorithm.