Fix DumpAsync to understand ContinuationWrapper (dotnet/coreclr#22913)

Fix DumpAsync to understand ContinuationWrapper (dotnet/coreclr#22913)

Continuations created while the debugger is attached or certain EventSource events are enabled end up getting wrapped in an extra ContinuationWrapper object that carries some additional information.  DumpAsync currently isn't unwrapping these but should.  This just teaches it to look for a known field name so that it can "see through" these wrappers while following async "stacks".

Commit migrated from https://github.com/dotnet/coreclr/commit/3a0367c75a9b5cebbcc2f2c9609aa05536ed921b