CMTK0005: report Array.Clear and Span<T>.Clear on value objects #270

Found in the weaving review of #229.

Array.Clear and Span<T>.Clear() set existing slots back to default, which CMTK0001 does not see since no default is written, and CMTK0005 does not report since nothing is created:

OrderId[] ids = [.. rows.Select(r => OrderId.From(r.Id))];
Array.Clear(ids);                        // every slot now a default OrderId, nothing reported
ids.AsSpan().Clear();                    // the same

Array.Fill(ids, default) and span.Fill(default) are already caught by CMTK0001, since they write default.

Proposal

CMTK0005 reports Array.Clear (each overload) and Span<T>.Clear() where the element is a value object, Option, Result or [RequireCustomInitialization] struct, unless a constant length of zero is given; resolved by symbol. The README's row then names clearing beside creating. A Warning reporting more needs no exception to decision 34. Whether this belongs in CMTK0005 (whose title is a collection "filled with default instances") or in a rule of its own is part of the decision.

Test

A CMTK0005 row per overload, a zero-length control, across TypeArgumentKinds.