10.x: translate RangeSet.Count (port of #484) #495

Problem

RangeSet.Count runs as SQL on main once #484 merges (PR #491). On release/10.x it runs in memory only.

Change

Cherry-pick PR #491's commits with -x into a PR against release/10.x:

• The placeholder in ValueRangesMemberTranslator, MultirangeCount, and its call from ValueRangesParameterBasedSqlProcessorFactory. It uses the same EF1001 nodes as Translate value set Intersect, Except, Add and a canonical Union for the non-text families with composed SQL #478's expander, which the Translate value set Intersect, Except, Add and a canonical Union for the non-text families with composed SQL #478 spike built on EF Core 10.
• RangeSetCountParityTests (an oracle, with the seed rangeset-count-of-a-null-multirange-is-zero.patch), RangeSetCountTranslationTests, the registration test, and the refreshed sql-processor-reuses-its-first-output.patch.
• The docs, claims E84, E85 and M06, translation-support.json and postgres-surface.json.
• The changelog rows go under [10.4.0] in the root, EF Core and EF Core NodaTime changelogs.

Done when

On release/10.x, the tests pass on the EF Core 10.0.0 floor and on CI's newest-patch leg, on PostgreSQL 16 and 18, and both seeds fail their oracles.

Release

### Added in 10.4.0. Fixed only on release/10.x, so close it by hand.