schematic editor: remove 10ms OnShow timer to reduce CPU load

Fixes: https://gitlab.com/kicad/code/kicad/-/issues/20385

common/draw_panel_gal.cpp

@@ -160,11 +160,7 @@ EDA_DRAW_PANEL_GAL::EDA_DRAW_PANEL_GAL( wxWindow* aParentWindow, wxWindowID aWin
     Connect( m_refreshTimer.GetId(), wxEVT_TIMER,
              wxTimerEventHandler( EDA_DRAW_PANEL_GAL::onRefreshTimer ), nullptr, this );
 
-    // Set up timer to execute OnShow() method when the window appears on the screen
-    m_onShowTimer.SetOwner( this );
-    Connect( m_onShowTimer.GetId(), wxEVT_TIMER,
-             wxTimerEventHandler( EDA_DRAW_PANEL_GAL::onShowTimer ), nullptr, this );
-    m_onShowTimer.Start( 10 );
+    Connect( wxEVT_SHOW, wxShowEventHandler( EDA_DRAW_PANEL_GAL::onShowEvent ), nullptr, this );
 }
 
 
@@ -650,11 +646,10 @@ void EDA_DRAW_PANEL_GAL::onRefreshTimer( wxTimerEvent& aEvent )
 }
 
 
-void EDA_DRAW_PANEL_GAL::onShowTimer( wxTimerEvent& aEvent )
+void EDA_DRAW_PANEL_GAL::onShowEvent( wxShowEvent& aEvent )
 {
     if( m_gal && m_gal->IsInitialized() && m_gal->IsVisible() )
     {
-        m_onShowTimer.Stop();
         OnShow();
     }
 }

include/class_draw_panel_gal.h

@@ -268,7 +268,7 @@ protected:
     void onLostFocus( wxFocusEvent& aEvent );
     void onIdle( wxIdleEvent& aEvent );
     void onRefreshTimer( wxTimerEvent& aEvent );
-    void onShowTimer( wxTimerEvent& aEvent );
+    void onShowEvent( wxShowEvent& aEvent );
 
     wxWindow*                m_parent;           ///< Pointer to the parent window
     EDA_DRAW_FRAME*          m_edaFrame;         ///< Parent EDA_DRAW_FRAME (if available)
@@ -288,9 +288,6 @@ protected:
     /// True when canvas needs to be refreshed from idle handler
     bool                     m_needIdleRefresh;
 
-    /// Timer used to execute OnShow() when the window finally appears on the screen.
-    wxTimer                  m_onShowTimer;
-
     /// Interface for drawing objects on a 2D-surface
     KIGFX::GAL*              m_gal;