!htp #16162 Upgrade server- and client-side HTTP APIs to "final style"

This PR clears #16162.
It currently builds on #16383, so ignore Björn's commit in your review.

As a temporary measure I have added a stub TCP API as described by #16166. This `TempTcp` stuff will go away when #16166 is cleared.
I guess the solution then is to keep the convenience method, mentioning that it is a shorthand and remove the active/passive part. Then we have:
 - the desired uniformity between TCP and HTTP as they both has this method
 - we have a simple usage entry point, which, points to the "advanced" usage in the doc