CMTK0003 misses a Task.WhenAny of Result tasks dropped without await #159

Found while folding #157 into #152's fix.

Problem

Task.WhenAny over tasks of results, dropped as a statement without await, compiles with no CMTK0003, while every neighbouring form is reported:

Task.WhenAll(LoadAsync(), LoadAsync());          // CMTK0003, collection of Results
await Task.WhenAll(LoadAsync(), LoadAsync());    // CMTK0003, collection of Results
await Task.WhenAny(LoadAsync(), LoadAsync());    // CMTK0003, Result
Task.WhenAny(LoadAsync(), LoadAsync());          // no diagnostic

(LoadAsync() returns Task<Result<int, Fault>>.) Measured on fix/cmtk0003-wrapped-assertions with an analyzer test that expected exactly the three diagnostics above, which passed.

Cause

WhenAny returns Task<Task<Result<…>>>. DroppedOutcome looks one task deep (PendingOutcome), so it finds a Task<Result> and no outcome; awaited, the statement drops a Task<Result>, which it does find.

Release

Ships in 2.3.0, by the maintainer's decision of 2026-10-29, in one PR with #152 and #157. The form is written with APIs 2.2.0 already had, so 2.3.0 reports code that built on 2.2.0; decision 118 and the Analyzers README's "What a new version may change" name this exception.

Fix

Tasks.PendingOutcome sees a task of a task of a result, so a dropped WhenAny, its conversion to a plain Task and Wait on it are reported. ReturnsItsStoredReceiver takes Task.WhenAny of tasks the caller holds, which completes with one of them and drops nothing. That also stops await Task.WhenAny(held, other); being reported, as 2.2.0 did.