Names of types and methods that are part of the runtime-async contract should be updated according to framework guidelines. #122512
Description
These types and methods are basically set in stone once they become part of ReadyToRun images. We should update the names to be more clear and descriptive as if they are public framework APIs.
Most of these are in AsyncHelpers. For example, ExecutionAndSyncBlockStore, FinalizeTaskReturningThunk, and AsyncHelpers.CompletedTask aren't great names or don't make sense.