Add toggleHV45Mode item to the measure tool's context menu

The behavior of the measure tool is influenced by the
horizontal/vertical/45-degree mode, but the context menu of the measure
tool lacks an option to toggle this mode. In contrast, the drawing
tools are also affected by this mode, and their context menu has the
item to toggle this mode.

pcbnew/tools/pcb_viewer_tools.cpp

@@ -51,6 +51,9 @@ bool PCB_VIEWER_TOOLS::Init()
     ctxMenu.AddItem( ACTIONS::cancelInteractive, activeToolCondition, 1 );
     ctxMenu.AddSeparator( 1 );
 
+    ctxMenu.AddCheckItem( PCB_ACTIONS::toggleHV45Mode, activeToolCondition, 2 );
+    ctxMenu.AddSeparator(                              activeToolCondition, 2 );
+
     frame()->AddStandardSubMenus( m_menu );
 
     return true;