Gui: Eliminate double->float truncations

Our GUI code uses a mix of floats and doubles to represent floating
point numbers, and in a few places interchanges them in a way that
causes an invisible loss of precision. Change the double precision
"default" values to float defaults, and use the appropriate value for
pi.

src/Gui/View3DInventorViewer.cpp

@@ -3606,7 +3606,7 @@ void View3DInventorViewer::alignToSelection()
             angle *= -1;
         }
 
-        using std::numbers::pi;
+        constexpr auto pi = std::numbers::pi_v<float>;
 
         // Make angle positive
         if (angle < 0) {