Allow menu records to be processed hierarchically by the UI driver

Nothing is actually processed in this way yet, but there is a new
assertion forbidding certain types of records from having children.

Because of this new assertion, our menutype tweaks must be moved up a
layer into internal/menus. They fit better there anyway.

internal/menus/menus.go

@@ -23,7 +23,7 @@ const (
 	TypeDoorHotspot     MenuType = 30 // Like a button I guess? "FONTTYPE is animation speed"
 	TypeDoorHotspot2    MenuType = 31 // Seems like a duplicate of the above? What's different?
 	TypeLineKbd         MenuType = 40
-	TypeThumb           MenuType = 45
+	TypeThumb           MenuType = 45 // A "thumb" appears to be a vertical slider
 	TypeLineBriefing    MenuType = 41
 	TypeInvokeButton    MenuType = 50
 	TypeDoorHotspot3    MenuType = 60 // Maybe? Appears in Arrange.mnu
@@ -67,6 +67,20 @@ var TextOverrides = map[string]map[string]string{
 	},
 }
 
+// FIXME: The menu is specified as type 2 (button) in these cases, which is
+// weird. Make it a menu for now.
+var TypeOverrides = map[string]map[string]MenuType{
+	"levelply": {
+		"2": TypeMenu,
+	},
+	"savegame": {
+		"2": TypeMenu,
+	},
+	"loadgame": {
+		"2": TypeMenu,
+	},
+}
+
 type Record struct {
 	Menu     *Menu
 	Parent   *Record
@@ -262,6 +276,13 @@ func setProperty(r *Record, k, v string) {
 		r.Id = vInt
 	case "MENUTYPE", "SUBMENUTYPE":
 		r.Type = MenuType(vInt)
+
+		// FIXME: Type override. Note that MENUID is specified first, so this works
+		if overrides, ok := TypeOverrides[r.Menu.Name]; ok {
+			if newType, ok := overrides[r.Path()]; ok {
+				r.Type = newType
+			}
+		}
 	case "ACTIVE":
 		r.Active = (vInt != 0)
 	case "SPRITEID":