Fix CreateProcessW failing when :directory is specified on Windows

[Catsquotl]

The dir-wide foreign string in create-process was missing the
:encoding :utf-16le parameter, while cmd-wide had it correctly set.
Since CreateProcessW expects UTF-16LE strings, passing a directory
would always cause the process creation to fail.

This broke M-x slime in Lem on Windows, which passes the buffer's
directory when starting the Lisp subprocess.

Fix: add :encoding :utf-16le to the dir-wide foreign string allocation.

The fix works, for full disclosure, Claude ai did most of the bug hunting and suggested fixes, I just copied and pasted through the process for a few hours