Create a BigRedButton struct, like CloseButton

The `BigRedButton` should be a real struct and component so that I can
query for it later.

I'm following the same API pattern as the `CloseButton` struct, in that
there is a spawner using the `Commands` (or `ChildSpawnerCommands`) and
the observer functions are static methods.

src/widgets/machines.rs

@@ -3,7 +3,7 @@ use bevy::{color::palettes::css::*, prelude::*, ui::Val::*};
 use crate::{
   game::machines::*,
   resources::UiTheme,
-  widgets::{machine_ui_base, spawn_big_red_button},
+  widgets::{BigRedButton, machine_ui_base},
 };
 
 impl CuttingMachine {
@@ -42,7 +42,7 @@ impl CuttingMachine {
           BackgroundColor(DARK_GRAY.into()),
           Pickable::default(),
         ))
-        .with_children(|cmds| spawn_big_red_button(cmds, "CUT"));
+        .with_children(|cmds| BigRedButton::spawn_big_red_button(cmds, "CUT"));
     });
   }
 }
@@ -82,7 +82,7 @@ impl RotatingMachine {
           BackgroundColor(DARK_GRAY.into()),
           Pickable::default(),
         ))
-        .with_children(|cmds| spawn_big_red_button(cmds, "TURN"));
+        .with_children(|cmds| BigRedButton::spawn_big_red_button(cmds, "TURN"));
     });
   }
 }