Avoid some unnecessary copying in Fformat etc.

Avoid some unnecessary copying in Fformat etc.

This patch is just for performance; it should not affect behavior.
On my platform, it made the microbenchmark (format "%S" load-path)
run about 45% faster.  It should also speed up calls like (message
"%s" STRING).
* src/callint.c (Fcall_interactively):
* src/dbusbind.c (XD_OBJECT_TO_STRING):
* src/editfns.c (Fmessage, Fmessage_box):
* src/xdisp.c (vadd_to_log, Ftrace_to_stderr):
Use styled_format instead of Fformat or Fformat_message,
to avoid unnecessary copying.
* src/editfns.c (styled_format): New arg NEW_RESULT.
All uses changed.  Reuse an input string if it has the
right value and if !NEW_RESULT.
* src/lisp.h (style_format): New decl.