Add JSON column support for default ordering

[SimonCropp]

OrderBy/ThenBy now accept a property path, so a property of a ToJson() mapped column can be used for default ordering.

builder.Entity<Order>()
    .OwnsOne(_ => _.Metadata, _ => _.ToJson());

builder.Entity<Order>()
    .OrderByDescending(_ => _.Metadata.Priority)
    .ThenBy(_ => _.Reference);

EF Core translates the path to a read of the JSON document:

ORDER BY CAST(JSON_VALUE([o].[Metadata], '$.Priority') AS int) DESC, [o].[Reference]

Paths of any depth work (_ => _.Info.Audit.Modified becomes '$.Audit.Modified'), and JSON properties mix with ordinary columns in the same chain. Everything else composes as before: the ordering is applied before Skip/Take/First, explicit ordering in a query still takes precedence, and inheritance, cross context conflict detection and redundant ordering detection all understand the dotted path.

Implementation

• New PropertyPath resolves a member chain rooted at the lambda parameter. OrderByClause walks that chain instead of building a single Expression.Property.
• ClauseMetadata stores the dotted path, so derived type replay, conflict detection across contexts and RedundantOrder keep working unchanged.

Two deliberate limits

Indexes are skipped for JSON paths. A JSON property is not a column of the entity's table, so there is nothing to name in HasIndex. This follows the existing string column behaviour: the index is skipped, the ordering still applies. A composite ordering is skipped whole when any one of its clauses reaches into JSON.

JSON collections keep document order. Include(_ => _.Tags.OrderBy(...)) over a ToJson() collection throws InvalidOperationException on a tracking query; it only works under AsNoTracking. Auto applying ordering there would break queries that work today, so IncludeOrderingApplicator now leaves JSON mapped collections alone. Without that guard, a CLR type used both as a regular entity and as a JSON collection elsewhere would hit exactly that failure.

Tests

Ten tests in JsonColumnTests.cs cover ordering, nesting, mixed chains, Take, index skipping, redundancy detection, requireOrderingForAllEntities against JSON owned types, and that a tracked Include over a JSON collection still works. Three Verify snapshots lock in the generated SQL.

Full suite passes in Release (139 tests), verified against SQL Server via LocalDb.