[RemoteAST] Enable a fallback where MetadataPromises can resolve themselves by means of the existing MetadataSP logic if the new style resolution fails. This is a useful intermediate stage as one converts things to the new API
[RemoteAST] Enable a fallback where MetadataPromises can resolve themselves by means of the existing MetadataSP logic if the new style resolution fails. This is a useful intermediate stage as one converts things to the new API

apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb,apple/swift-lldb