Prepare for boost::url upgrade

The new boost URL now interops properly with std::string_view, which is
great, and cleans up a bunch of mediocre code to convert one to another.
It has also been pulled into boost-proper, so we no longer need a
boost-url dependency that's separate.

Unfortunately, boost url makes these improvements by changing
boost::string_view for boost::urls::const_string, which causes us to
have some compile errors on the missing type.

The bulk of these changes fall into a couple categories, and have to be
executed in one commit.
string() is replaced with buffer() on the url and url_view types
boost::string_view is replaced by std::string_view for many times, in
many cases removing a temporary that we had in the code previously.

Tested: Code compiles with boost 1.81.0 beta.
Redfish service validator passes.
Pretty good unit test coverage for URL-specific use cases.

Signed-off-by: Ed Tanous <edtanous@google.com>
Change-Id: I8d3dc89b53d1cc390887fe53605d4867f75f76fd
diff --git a/http/http_request.hpp b/http/http_request.hpp
index deaba31..d203077 100644
--- a/http/http_request.hpp
+++ b/http/http_request.hpp
@@ -116,16 +116,14 @@
   private:
     bool setUrlInfo()
     {
-        auto result = boost::urls::parse_relative_ref(
-            boost::urls::string_view(target().data(), target().size()));
+        auto result = boost::urls::parse_relative_ref(target());
 
         if (!result)
         {
             return false;
         }
         urlView = *result;
-        url = std::string_view(urlView.encoded_path().data(),
-                               urlView.encoded_path().size());
+        url = urlView.encoded_path();
         return true;
     }
 };