feat: readds transfer encoding to the header list.

[jcchavezs]

Transfer-Encoding property turns into a request field by the http handler, this commit adds it back for the sake of correctness.

Still trying to figure out how to write the test.

[codefromthecrypt]

for unit test, maybe something like Test_host_GetProtocolVersion but GetRequestHeaderValues. Then in the test make it a table-driven test which has a field req *http.Request and in that you can set the special Host and TransferEncoding.

TCK would be good insulation as well, even though even if TCK is updated, the above unit test should be there. testRunner.testGetHeaderValuesRequest is awkward to do host/trasnfer encoding, so there after the table test, you could make separate calls like r.t.Run("host", func(t *testing.T) { with explicit impls which probably need to construct the http client requests.

[codefromthecrypt]

I will try to land the intended change this week, in this PR or another

[codefromthecrypt]

closing as I don't have time to polish this and stale PRs don't tend to proceed. Someone can finish this including tests in another PR if they choose.