patch 8.2.0559: clearing a struct is verbose

Problem:    Clearing a struct is verbose.
Solution:   Define and use CLEAR_FIELD() and CLEAR_POINTER().
diff --git a/src/os_mswin.c b/src/os_mswin.c
index faa4c99..1c987c2 100644
--- a/src/os_mswin.c
+++ b/src/os_mswin.c
@@ -1338,7 +1338,7 @@
     int			i;
 
     bUserAbort = &(psettings->user_abort);
-    vim_memset(&prt_dlg, 0, sizeof(PRINTDLGW));
+    CLEAR_FIELD(prt_dlg);
     prt_dlg.lStructSize = sizeof(PRINTDLGW);
 # if !defined(FEAT_GUI) || defined(VIMDLL)
 #  ifdef VIMDLL
@@ -1467,7 +1467,7 @@
     /*
      * Initialise the font according to 'printfont'
      */
-    vim_memset(&fLogFont, 0, sizeof(fLogFont));
+    CLEAR_FIELD(fLogFont);
     if (get_logfont(&fLogFont, p_pfn, prt_dlg.hDC, TRUE) == FAIL)
     {
 	semsg(_("E613: Unknown printer font: %s"), p_pfn);
@@ -1562,7 +1562,7 @@
     {
 	DOCINFOW	di;
 
-	vim_memset(&di, 0, sizeof(di));
+	CLEAR_FIELD(di);
 	di.cbSize = sizeof(di);
 	di.lpszDocName = wp;
 	ret = StartDocW(prt_dlg.hDC, &di);
@@ -2881,7 +2881,7 @@
 # if defined(FEAT_GUI_MSWIN)
 	CHOOSEFONTW	cf;
 	// if name is "*", bring up std font dialog:
-	vim_memset(&cf, 0, sizeof(cf));
+	CLEAR_FIELD(cf);
 	cf.lStructSize = sizeof(cf);
 	cf.hwndOwner = s_hwnd;
 	cf.Flags = CF_SCREENFONTS | CF_FIXEDPITCHONLY | CF_INITTOLOGFONTSTRUCT;