patch 8.0.1343: MS-Windows: does not show colored emojis

Problem:    MS-Windows: does not show colored emojis.
Solution:   Implement colored emojis. Improve drawing speed. Make 'taamode'
            work. (Taro Muraoka, Yasuhiro Matsumoto, Ken Takata, close #2375)

src/gui_dwrite.h

@@ -4,6 +4,7 @@
  *
  * Contributors:
  *  - Ken Takata
+ *  - Yasuhiro Matsumoto
  *
  * Copyright (C) 2013 MURAOKA Taro <koron.kaoriya@gmail.com>
  * THIS FILE IS DISTRIBUTED UNDER THE VIM LICENSE.
@@ -54,12 +55,10 @@ void DWrite_Init(void);
 void DWrite_Final(void);
 
 DWriteContext *DWriteContext_Open(void);
-void DWriteContext_BeginDraw(DWriteContext *ctx);
 void DWriteContext_BindDC(DWriteContext *ctx, HDC hdc, RECT *rect);
 void DWriteContext_SetFont(DWriteContext *ctx, HFONT hFont);
 void DWriteContext_DrawText(
 	DWriteContext *ctx,
-	HDC hdc,
 	const WCHAR* text,
 	int len,
 	int x,
@@ -67,8 +66,12 @@ void DWriteContext_DrawText(
 	int w,
 	int h,
 	int cellWidth,
-	COLORREF color);
-void DWriteContext_EndDraw(DWriteContext *ctx);
+	COLORREF color,
+	UINT fuOptions,
+	CONST RECT *lprc,
+	CONST INT * lpDx);
+void DWriteContext_FillRect(DWriteContext *ctx, RECT *rc, COLORREF color);
+void DWriteContext_Flush(DWriteContext *ctx);
 void DWriteContext_Close(DWriteContext *ctx);
 
 void DWriteContext_SetRenderingParams(