Fix extra newline from nimpretty when used with --stdin (#24951)

Using `echo` to print file contents to stdout automatically adds a
newline at the end of the file contents. When using nimpretty to auto
format files on save in some editors which replace the file contents
with the formatted ones this means that with every save/format operation
an additional newline is added to the end of the file. Using
`stdout.write` does not automatically add a newline at the end
preventing this issue.

Fixes #24950

(cherry picked from commit c1e6cf812f)

nimpretty/nimpretty.nim

@@ -111,7 +111,7 @@ proc handleStdinInput(opt: PrettyOptions) =
 
   prettyPrint(path, path, opt)
 
-  echo(readAll(cfile))
+  stdout.write(readAll(cfile))
 
   close(cfile)
   removeFile(path)