Allow suppressing warnings from wxImage::LoadFile()

Add wxImage::SetLoadFlags() and static SetDefaultLoadFlags() to allow
suppressing the warning messages that can be logged when loading some files,
notably PNG ones with invalid sRGB profiles which, unfortunately, seem to be
rather common and result in annoying warnings about them with libpng 1.6+.

Closes #15331.

include/wx/image.h

@@ -408,6 +408,22 @@ public:
     // colour given.
     bool ConvertColourToAlpha( unsigned char r, unsigned char g, unsigned char b );
 
+    // Methods for controlling LoadFile() behaviour. Currently they allow to
+    // specify whether the function should log warnings if there are any
+    // problems with the image file not completely preventing it from being
+    // loaded. By default the warnings are logged, but this can be disabled
+    // either globally or for a particular image object.
+    enum
+    {
+        Load_Verbose = 1
+    };
+
+    static void SetDefaultLoadFlags(int flags);
+    static int GetDefaultLoadFlags();
+
+    void SetLoadFlags(int flags);
+    int GetLoadFlags() const;
+
     static bool CanRead( const wxString& name );
     static int GetImageCount( const wxString& name, wxBitmapType type = wxBITMAP_TYPE_ANY );
     virtual bool LoadFile( const wxString& name, wxBitmapType type = wxBITMAP_TYPE_ANY, int index = -1 );