Differentiate between a Distribution which statisfies any required Distribution vs. none.

[msirek]

Currently, in the optimizer, RelExpr.ProvidedPhysical().Distribution indicates which regions a relation accesses. An empty distribution means the input can provide any distribution required by the consumer, but can also sometimes mean all regions are accessed (can provide no required distribution except the distribution which includes all regions). This issue is opened to differentiate between these cases in the code, and to also make sure a distribution is always built for all expressions (VALUES clauses, for example, which can be considered local to the gateway region).

Jira issue: CRDB-18850

[github-actions]

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