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.

interface/wx/image.h

@@ -1373,6 +1373,12 @@ public:
     /**
         Loads an image from an input stream.
 
+        If the file can't be loaded, this function returns false and logs an
+        error using wxLogError(). If the file can be loaded but some problems
+        were detected while doing it, it can also call wxLogWarning() to notify
+        about these problems. If this is undesirable, use SetLoadFlags() to
+        reset @c Load_Verbose flag and suppress these warnings.
+
         @param stream
             Opened input stream from which to load the image.
             Currently, the stream must support seeking.
@@ -1605,6 +1611,47 @@ public:
     void SetData(unsigned char* data, int new_width, int new_height,
                  bool static_data = false);
 
+    /**
+        Sets the default value for the flags used for loading image files.
+
+        This method changes the global value of the flags used for all the
+        subsequently created wxImage objects by default. It doesn't affect the
+        already existing objects.
+
+        By default, the global flags include @c Load_Verbose flag value.
+
+        @see LoadFile(), SetLoadFlags(), GetDefaultLoadFlags()
+
+        @since 3.1.0
+     */
+    static void SetDefaultLoadFlags(int flags);
+
+    /**
+        Sets the flags used for loading image files by this object.
+
+        The flags will affect any future calls to LoadFile() for this object.
+        To change the flags for all image objects, call SetDefaultLoadFlags()
+        before creating any of them.
+
+        Currently the only defined flag is @c Load_Verbose which determines if
+        the non-fatal (i.e. not preventing the file from being loaded
+        completely) problems should result in the calls to wxLogWarning()
+        function. It is recommended to customize handling of these warnings by
+        e.g. defining a custom log target (see @ref overview_log), but if such
+        warnings should be completely suppressed, clearing this flag provides a
+        simple way to do it, for example:
+        @code
+            wxImage image;
+            image.SetLoadFlags(image.GetLoadFlags() & ~wxImage::Load_Verbose);
+            image.LoadFile(...);
+        @endcode
+
+        @see LoadFile(), SetLoadFlags(), GetLoadFlags()
+
+        @since 3.1.0
+     */
+    void SetLoadFlags(int flags);
+
     /**
         Specifies whether there is a mask or not.
 
@@ -1852,6 +1899,15 @@ public:
     */
     static bool CanRead(wxInputStream& stream);
 
+    /**
+        Returns the currently used default file load flags.
+
+        See SetDefaultLoadFlags() for more information about these flags.
+
+        @since 3.1.0
+     */
+    static int GetDefaultLoadFlags();
+
     //@{
     /**
         If the image file contains more than one image and the image handler is
@@ -1909,6 +1965,15 @@ public:
     */
     static wxString GetImageExtWildcard();
 
+    /**
+        Returns the file load flags used for this object.
+
+        See SetLoadFlags() for more information about these flags.
+
+        @since 3.1.0
+     */
+    int GetLoadFlags() const;
+
     /**
         Converts a color in RGB color space to HSV color space.
     */