bug#81506: [PATCH] Extend w32 window events to expose IME composition string interface

hello.

This patch adds IME composition string support for the
MS-Windows (w32) platform.

Add WM_IME_COMPOSITION event processing

Handle the composition string from IME and hide the
composition string window.  Add an Elisp hook to deliver the
composition result to Lisp code.

* src/w32fns.c (w32_wnd_proc): Hide composition string window.
* src/w32term.c (w32_read_socket): Read composition result to Lisp code.

After setting up the hook, the composed string can be drawn using Elisp
overlays.
I have created a separate repository to demonstrate the functionality of
this patch:

https://github.com/zHaOdANiuu/emacs-w32-draw-preedit.patch

I am in the process of completing the FSF copyright assignment.