[3.12] gh-119452: Fix a potential virtual memory allocation denial of service in http.server (GH-142216) (#142297)

[3.14] gh-119452: Fix a potential virtual memory allocation denial of service in http.server (GH-142216)

The CGI server on Windows could consume the amount of memory specified
in the Content-Length header of the request even if the client does not
send such much data. Now it reads the POST request body by chunks,
therefore the memory consumption is proportional to the amount of sent
data.
(cherry picked from commit 0e4f4f1a4633f2d215fb5a803cae278aeea31845)

Co-authored-by: Serhiy Storchaka <storchaka@gmail.com>