Win32: Use helper window to load WGL extensions

This removes window re-creation logic by performing the initial context
creation on the helper window, simplifying both window and context
creation and paving the way for attaching to existing window handles
without compromising on context or framebuffer hint support.

src/wgl_context.h

@@ -82,6 +82,7 @@ typedef HGLRC (WINAPI * PFNWGLCREATECONTEXTATTRIBSARBPROC)(HDC,HGLRC,const int*)
 typedef HGLRC (WINAPI * WGLCREATECONTEXT_T)(HDC);
 typedef BOOL (WINAPI * WGLDELETECONTEXT_T)(HGLRC);
 typedef PROC (WINAPI * WGLGETPROCADDRESS_T)(LPCSTR);
+typedef HDC (WINAPI * WGLGETCURRENTDC_T)(void);
 typedef BOOL (WINAPI * WGLMAKECURRENT_T)(HDC,HGLRC);
 typedef BOOL (WINAPI * WGLSHARELISTS_T)(HGLRC,HGLRC);
 
@@ -89,6 +90,7 @@ typedef BOOL (WINAPI * WGLSHARELISTS_T)(HGLRC,HGLRC);
 #define wglCreateContext _glfw.wgl.CreateContext
 #define wglDeleteContext _glfw.wgl.DeleteContext
 #define wglGetProcAddress _glfw.wgl.GetProcAddress
+#define wglGetCurrentDC _glfw.wgl.GetCurrentDC
 #define wglMakeCurrent _glfw.wgl.MakeCurrent
 #define wglShareLists _glfw.wgl.ShareLists
 
@@ -118,6 +120,7 @@ typedef struct _GLFWlibraryWGL
     WGLCREATECONTEXT_T                  CreateContext;
     WGLDELETECONTEXT_T                  DeleteContext;
     WGLGETPROCADDRESS_T                 GetProcAddress;
+    WGLGETCURRENTDC_T                   GetCurrentDC;
     WGLMAKECURRENT_T                    MakeCurrent;
     WGLSHARELISTS_T                     ShareLists;
 
@@ -147,8 +150,5 @@ void _glfwTerminateWGL(void);
 GLFWbool _glfwCreateContextWGL(_GLFWwindow* window,
                                const _GLFWctxconfig* ctxconfig,
                                const _GLFWfbconfig* fbconfig);
-int _glfwAnalyzeContextWGL(_GLFWwindow* window,
-                           const _GLFWctxconfig* ctxconfig,
-                           const _GLFWfbconfig* fbconfig);
 
 #endif // _glfw3_wgl_context_h_