Await middleware responses

[katywings]

Currently if a start middleware returns a result, the internal sendWebResponse is not being called with await. This becomes a problem if the result type is of asynchronous nature (e.g. a stream) as h3 will not wait for it to finish and proceed with the next entry in the chain.

Awaiting sendWebResponse solves some cases, but not all of them (#1588 (comment)). A discussion about rewriting the start middleware from the current h3 hooks approach to proper h3 middleware is recommended. Follow ups: #1743 and #1523.