Fix StreamReader to pass cancellation token into ReadBufferAsync (#27464)
Fix StreamReader to pass cancellation token into ReadBufferAsync (#27464)

ReadAsyncInternal is correctly passing its token into the two call sites where it delegates directly to the underlying stream, but in one place it calls through ReadBufferAsync, which is currently not defined to take a token.  Fix that, and pass the token through.

Signed-off-by: dotnet-bot <03c4cb6107ae99956a7681f2c97ff7104809a2bd@microsoft.com>

shimingsg/corefx,ericstj/corefx,shimingsg/corefx,shimingsg/corefx,shimingsg/corefx,ericstj/corefx,shimingsg/corefx,shimingsg/corefx,ericstj/corefx,ericstj/corefx,ericstj/corefx,ericstj/corefx,ericstj/corefx,shimingsg/corefx