[pdevito3]

Fixes #201

Problem

A filter on a collection property failed for some collection types:

• ^$ and !^$ failed on IReadOnlyList<T>, IReadOnlyCollection<T>, HashSet<T>, arrays, and classes that inherit from List<T>.
• == and the other comparison operators failed on a direct collection property of every type, List<T> included. Only a nested path such as Ingredients.Name == "salt" worked.

Change

• IsCollection() and GetCollectionElementType() in QueryKit/Extensions.cs read IEnumerable<T> from the interfaces of the type. They replace two copies of the check in FilterParser and PropertyResolver, and the checks in each operator.
• A comparison on a direct collection property matches when any element matches. % makes it match when all elements match. This is the same as a nested path.
• Tags == null and Tags != null check the property for null. Ingredients.Name == null keeps its old meaning: any element is null.
• != on a collection emits Any(z => !(z == value)). EF Core 10 with Npgsql can not translate Any(z => z != value) on a primitive collection. Both forms give the same SQL: t.value <> 'dinner'.

Behavior change: the expression text for != and !=* on a nested path changed from z != "flour" to Not((z == "flour")). The results do not change.

Tests

• QueryKit.UnitTests/CollectionTypeFilterTests.cs: 8 collection types, each with the same operators. Also number collections, null checks, and nested paths. Before the fix, 89 cases failed.
• QueryKit.IntegrationTests/Tests/CollectionTypeFilterTests.cs: a projection from an EF entity to a DTO with IReadOnlyList<string> and IReadOnlyCollection<string>, filtered on Postgres. This test found the != translation fault.
• The verify-querykit harness model has a new string[] Labels column (text[]). Ten filters on Tags and on Labels gave the same rows in memory and on Postgres.

Out of scope

• ^^ (in) on a collection property: Support the in operator (^^) on a collection property #202.
• A sort on a collection property in a DTO fails in EF translation.