Treat lookups by key as bounded, and skip Includes EF ignores

[SimonCropp]

Two false positives, both found by comparing the checks with the rules in LinqContraband (LC031 and LC049).

Lookups by key are bounded

RejectUnbounded fired for Employees.Where(_ => _.Id == id), which returns at most one row. A Where that compares a key with a value now bounds the query like a Take:

• Other conditions can be added with &&. With ||, each side has to be a lookup. A composite key needs every part compared.
• The key is the primary key or an alternate key, read from the model, so shadow keys and EF.Property work. A unique index does not count: a filter can make it unique among only some rows, and a column that allows null can hold null in many rows.
• ids.Contains(_.Id) returns a row for each value, so it is only bounded when MaxInValues is set. The log and throw levels each decide that with their own MaxInValues, so the shape carries the unbounded row types both with lists limited and without.
• Only the rows of a DbSet can be looked up, with only filters, ordering, Skip, Take, Distinct, OfType and options such as Include between them. After Concat, SelectMany, Join or Select, or on FromSql, the same key can be in many rows.

Includes Entity Framework ignores are not counted

MaxSingleQueryCollections counted 2 for Departments.Include(_ => _.Employees).Include(_ => _.Projects).Select(_ => _.Name), which loads no collections. An Include before a Select that returns no entity, or an aggregate like Count(), is now skipped. A projection that could return an entity, including one passing it to a method, keeps the Includes counted. MaxIncludes and MaxIncludeDepth still count every Include as written.

Checked against Entity Framework on six queries: in each, the count agrees with Entity Framework's MultipleCollectionIncludeWarning and with the joins in the SQL it generates.

Tests

38 new tests, in KeyLookupTests (with a KeyContext model for composite, alternate, unique index and derived keys), UnboundedTests and ShapeTests. The full suite passes locally, 216 tests including the LocalDB ones.