Convert `call System.Runtime.CompilerServices.AsyncHelpers.Await(value)`
to the IL Await instruction whenever DecompilerSettings.RuntimeAsync is
enabled. The state-machine async pipeline (AsyncAwaitDecompiler) already
produces the IL Await for downstream transforms (UsingTransform's
MatchDisposeBlock pattern-matches on it via UnwrapAwait); doing the
conversion in EarlyExpressionTransforms gives the runtime-async output
the same canonical shape before any consumer runs.
Siegfried Pammer