v1.17: sleep instead of drop when stream rate exceeded limit; (backport of #939)

[mergify]

Problem

Currently we are dropping the stream right away when the stream rate limit is being exceeded. The problem is the client can retry right away. In addition, the stream might have been received and can be used, dropping it waste resources.

Summary of Changes

Change to sleep instead of drop. Thanks to @alessandrod -- we sleep based on the estimated time to elapse to appease the rate limit and consider the RTT for the connection.

Fixes #

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This is an automatic backport of pull request #939 done by [Mergify](https://mergify.com).

[mergify]

Cherry-pick of 137a982 has failed:

On branch mergify/bp/v1.17/pr-939
Your branch is up to date with 'origin/v1.17'.

You are currently cherry-picking commit 137a982a1e.
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Unmerged paths:
  (use "git add/rm <file>..." as appropriate to mark resolution)
	both modified:   streamer/src/nonblocking/quic.rs
	deleted by us:   streamer/src/nonblocking/stream_throttle.rs

no changes added to commit (use "git add" and/or "git commit -a")

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[lijunwangs]

Superseded by #991