Add response status code test

[alex-james-dev]

• Created a new test group response status line to test that package:http clients correctly process the response status line.

• Added a new test without status code to the response status line test group.

• The without status code test checks that package:http clients can handle an HTTP response status line with a missing status code, e.g. HTTP/1.1 OK.

• cronet_http is failing without status code test, we are skipping the test until we fix this issue: cronet_http is failing "without status code" test #1013.

• Created a new test server response_status_line_server.dart that receives a status line from the client and sets this as the response status line.

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[brianquinlan]

Please update the PR message.

[brianquinlan]

cronet_http fails this test - maybe mark is as skipped with a reason like 'currently failing in cronet_http, see XXX` where XXX is a link to an issue that you file against cronet_http ;-)

[alex-james-dev]

Hey @brianquinlan,

• The PR message has been updated.

• An issue has been filed against cronet_http because it fails the without status code test in the response status line test group: cronet_http is failing "without status code" test #1013.

• Until we fix this issue, we will skip the without status code test and output the following message instead:

Enable after https://github.com/dart-lang/sdk/issues/ is fixed

This PR is now ready for review! 🎉