[format.functions] Add "std::move" around "out" (#5069)

This fixes a misapplication of the resolution of LWG 3539.

Author: mordante

source/utilities.tex

@@ -21506,7 +21506,7 @@
 \effects
 Equivalent to:
 \begin{codeblock}
-return vformat_to(out, fmt.@\exposid{str}@, make_format_args(args...));
+return vformat_to(std::move(out), fmt.@\exposid{str}@, make_format_args(args...));
 \end{codeblock}
 \end{itemdescr}
 
@@ -21536,7 +21536,7 @@
 \effects
 Equivalent to:
 \begin{codeblock}
-return vformat_to(out, loc, fmt.@\exposid{str}@, make_format_args(args...));
+return vformat_to(std::move(out), loc, fmt.@\exposid{str}@, make_format_args(args...));
 \end{codeblock}
 \end{itemdescr}