Add private header for wxWebViewChromium Mac-specific functions

Instead of just declaring the function inline in the common code, do it
in a header included from both common C++ and Mac Objective C++ sources.

No real changes.

include/wx/osx/private/webview_chromium.h

@@ -0,0 +1,16 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/osx/private/webview_chromium.h
+// Purpose:     Functions used in wxWebViewChromium Mac implementation
+// Author:      Vadim Zeitlin
+// Created:     2023-09-05
+// Copyright:   (c) 2023 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_OSX_PRIVATE_WEBVIEW_CHROMIUM_H_
+#define _WX_OSX_PRIVATE_WEBVIEW_CHROMIUM_H_
+
+// Called during startup to add CefAppProtocol support to wxNSApplication.
+void wxWebViewChromium_InitOSX();
+
+#endif // _WX_OSX_PRIVATE_WEBVIEW_CHROMIUM_H_

src/common/webview_chromium.cpp

@@ -29,6 +29,10 @@
 #include <gdk/gdkx.h>
 #endif
 
+#ifdef __WXOSX__
+#include "wx/osx/private/webview_chromium.h"
+#endif
+
 #ifdef __VISUALC__
 #pragma warning(push)
 #pragma warning(disable:4100)
@@ -1238,10 +1242,6 @@ bool SchemeHandler::ReadResponse(void* data_out,
     return has_data;
 }
 
-#ifdef __WXOSX__
-void wxWebViewChromium_InitOSX();
-#endif
-
 namespace
 {
 

src/osx/webview_chromium.mm

@@ -12,6 +12,9 @@
 #import "Cocoa/Cocoa.h"
 #include <objc/runtime.h>
 #include "wx/log.h"
+
+#include "wx/osx/private/webview_chromium.h"
+
 #import "include/cef_application_mac.h"
 
 /*