[time.hms.nonmembers] Finish rebase on std::format: rewrite hh_mm_ss

operator<< in terms of format rather than using (removed) old formatting
terminology.

Author: zygoloid

source/time.tex

@@ -8037,12 +8037,12 @@
 \begin{itemdescr}
 \pnum
 \effects
-Outputs to \tcode{os} according to the format \tcode{"\%T"}\iref{time.format}.
-If \tcode{hms.is_negative()}, the output is preceded with \tcode{'-'}.
-
-\pnum
-\returns
-\tcode{os}.
+Equivalent to:
+\begin{codeblock}
+if (hms.is_negative())
+  os << @\placeholder{STATICALLY-WIDEN}@<charT>("-");
+return os << format(os.getloc(), @\placeholder{STATICALLY-WIDEN}@<charT>("{:%T}"), hms);
+\end{codeblock}
 
 \pnum
 \begin{example}