Connection shutdown with buffered data

[TingDaoK]

Issue #, if available:

• Another similar fix to TLS deliver buffer data during shutdown aws-c-io#650 and Fix bug where last few bytes on socket go unread aws-c-io#642
• We have buffer in HTTP connection, and connection had different window than the stream and it already read to the buffer, even if the stream has 0 window.
• So, when we read the last bytes into connection buffer, and channel starts to shutdown, the buffered data will be unread and stream will fail, while it should wait until those data to be read.

Description of changes:

• very similar fix to TLS deliver buffer data during shutdown aws-c-io#650, put the channel shutdown on hold until the buffer data read from downstream.
• Also a TODO from adapt change from "TLS deliver buffer data during shutdown" #474, which we thought it only affects websocket, as it's the only downstream for HTTP/1.1 connection, however, since the difference of the window for connection and stream, it affects the HTTP as well. :(

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 97.14286% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.45%. Comparing base (b5684c7) to head (c9cfa04).
Report is 28 commits behind head on main.

Files with missing lines	Patch %	Lines
source/h1_connection.c	97.14%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #482      +/-   ##
==========================================
- Coverage   79.51%   79.45%   -0.07%     
==========================================
  Files          27       27              
  Lines       11661    11689      +28     
==========================================
+ Hits         9272     9287      +15     
- Misses       2389     2402      +13     

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