Replace [Press {button} to toggle gameplay] by freeze/unfreeze

This is both easier for translators ("toggle" can be an annoying word)
and is useful in general because you can tell if gameplay is frozen
without having to have anything in the room that should normally be
moving but isn't.

I didn't follow the rule in lang/README-programmers.txt to keep the
original string around as ***OUTDATED*** in this case, since I know
only Arabic has it translated - we can just tell the Arabic translators
on Discord that this string was replaced.

desktop_version/src/LevelDebugger.cpp

@@ -445,10 +445,19 @@ namespace level_debugger
             }
         }
 
+        const char* text;
+        if (should_pause)
+        {
+            text = loc::gettext("[Press {button} to unfreeze gameplay]");
+        }
+        else
+        {
+            text = loc::gettext("[Press {button} to freeze gameplay]");
+        }
         char buffer[SCREEN_WIDTH_CHARS + 1];
         vformat_buf(
             buffer, sizeof(buffer),
-            loc::gettext("[Press {button} to toggle gameplay]"),
+            text,
             "button:str",
             "TAB"
         );