Tool windows test suite; drop visual_novel_core dependency

- test_suites/windows (--itest=tools_windows [--shots=<dir>]) opens every
  tool window, fails on any engine error logged meanwhile, drives the
  map/interactive/light canvases and can save a screenshot per window.
- The tools need the engine mods only; visual_novel_core is no longer a
  dependency (the Novel Editor collection brings the content).

manifest.json

@@ -8,5 +8,8 @@
   "sources": [
     "src/**/*.cs"
   ],
-  "depends": ["visual_novel_core>=1", "dialog_base>=1", "interactive_base>=1", "time_base>=1", "map_base>=1", "interface>=1"]
+  "depends": ["dialog_base>=1", "interactive_base>=1", "time_base>=1", "map_base>=1", "interface>=1"],
+  "test_suites": [
+    {"id": "windows", "activate": ["--itest=tools_windows"]}
+  ]
 }