[CaffeinatedCoder]

Closes #228

Stacked on #233 (#227), which changes the same file: merge #233 first, then retarget this to release/2.3.1.

Problem

DefaultFilledCollectionAnalyzer.AnalyzeInvocation looked only at generic calls with one type argument (GC.AllocateArray, GC.AllocateUninitializedArray, Array.Resize). Array.CreateInstance(typeof(Plain), 3) (one to three dimensions, params int[], params long[], with lower bounds), Array.CreateInstanceFromArrayType(typeof(Plain[]), 3) and ArrayPool<Plain>.Shared.Rent(3) create the same default slots and got nothing.

Change

• DefaultFilledCollectionAnalyzer.cs: the two factories are reported when a typeof names the element (for CreateInstanceFromArrayType, the element of the array type); a Type in a variable stays silent. Rent is recognised on ArrayPool<T> or an override of it, T the element. One Lengths reads every int/long length parameter and the elements of a params or written-out array of them, never lowerBounds, so CMTK0005 reports a multidimensional array with a zero dimension, such as new Plain[0, 2], which holds no element #227's rule holds for every form: a constant zero in any dimension stays silent.
• Analyzers README: the CMTK0005 section names the new forms and says a Type variable isn't reported; claim K05-a-factory-given-a-typeof holds it.
• CHANGELOG: a line under 2.3.1's Changed, since a warnings-as-errors build can now fail. A Warning that reports more needs no exception to decision 34.

Tests

• The_array_factories_and_the_pool_report: every CreateInstance/CreateInstanceFromArrayType overload that takes a length, Rent on the shared pool, on ArrayPool<T>.Create() and on a derived pool, an Option<int> element and a typeof(T) of a constrained parameter.
• The_array_factories_with_a_zero_length_or_an_unknown_type_stay_silent: a zero-length control for each form (in each dimension, in a params list, beside lower bounds, long), a Type variable, GetType(), typeof(Plain?), typeof(int), typeof(Plain[]), ArrayPool<int> and Activator.CreateInstance.
• The_factories_judge_each_kind_as_the_generic_allocator_does: Rent's T and the typeof element across TypeArgumentKinds (79 kinds); each reports exactly where GC.AllocateArray<K> does, with a value-object struct as the positive control and a compile-error check so no row passes vacuously.
• Reverting the source fails the forms row and the three reporting kinds. Seeds: dropping the zero check fails the three zero rows; reading the lower bounds as lengths fails the forms row; skipping an array of lengths fails the silent row.
• Analyzers (3,772), Conventions (2,016), Samples (150) and Oracles (51) green locally through tools/BuildVerdict.

CollectionsMarshal.SetCount is #229 (2.4.0) and out of scope.

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