Split out adding of individual request headers into a switch. Check
the connection http version only on fresh connections, use separate
methods.
Add TE: header directly without allocation. Add bit for indicating
Connection: header has been added and custom headers should not do
that again.
Closes#18444
The base64 sections were added in a time when there was no other way to
do these tests. Now we remove them again to make less "hidden" data in
the test suite.
For several test cases we instead then provide a sequence of binary
octets which is not really better, but I have tried to minimize them.
Closes#16816
The threee tags `<name>`, `</name>` and `<command>` were frequently used
with a leading space that this removes. The reason this habbit is so
widespread in testcases is probably that they have been copy and pasted.
Hence, fixing them all now might curb this practice from now on.
Closes#12028
