Remove borders and paddings from native controls on Linux (#14873)

* init

* update

* Update SpinInput.cpp

* possible fix for em_unit

* button alignment

* match titlebar height

* revert em_value for macOS and Windows

* Update GUI_Utils.hpp

* Merge branch 'main' into linux-black-borders-2

* Revert "button alignment"

This reverts commit 3fc7461071.

* Revert "match titlebar height"

This reverts commit c4aa1d9f1e.

* revert dpi changes

* match platform tags

* remove radio box borders

* Fix code indent

src/slic3r/GUI/wxExtensions.cpp

@@ -1022,6 +1022,10 @@ ScalableButton::ScalableButton( wxWindow *          parent,
         m_width = size.x * 10 / em;
         m_height= size.y * 10 / em;
     }
+
+#ifdef __WXGTK__
+    Slic3r::GUI::RemoveButtonBorder(this);
+#endif
 }