Add wxGrid::RefreshAttr() method to force attribute refresh.

A cached attribute may continue to be used even though the attribute returned
by a custom wxGridCellAttrProvider has changed so add a method to force wxGrid
to update the attribute by forgetting the cached copy.

Closes #12406.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@65451 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/generic/grid.cpp

@@ -7259,6 +7259,13 @@ void wxGrid::ClearAttrCache()
     }
 }
 
+void wxGrid::RefreshAttr(int row, int col)
+{
+    if ( m_attrCache.row == row && m_attrCache.col == col )
+        ClearAttrCache();
+}
+
+
 void wxGrid::CacheAttr(int row, int col, wxGridCellAttr *attr) const
 {
     if ( attr != NULL )