Add include_httplib.cc to the main test executable (already done in
Makefile), and add include_windows_h.cc to the main test executable on
Windows to test if including windows.h conflicts with httplib.h.
* Add workflow_dispatch with Google Test filter
Add the workflow_dispatch trigger to the test.yaml workflow. Includes an
input for an optional Google Test filter pattern.
* Add OS selection to workflow_dispatch
* Fix wording
Consider Content-Length and Transfer-Encoding headers when determining
whether to expect content. Don't handle the HTTP/2 connection preface
pseudo-method PRI.
Fixes#2028.