Redesign invalid node indicator (#358)

* nit

* Remove unused code

Gradient can (and should) be impl. directly by caching a CanvasGradient.

* nit

* nit - Refactor

* Remove redundant code

* Add line width & colour options to shape stroke

* Rename drawSelectionBounding to strokeShape

* nit - Doc

* Fix rounded corners not scaling with padding

* Optimise node badge draw

* Redesign invalid node visual indication

Customisable boundary indicator now used, replacing red background.

* Update snapshot

---------

Co-authored-by: huchenlei <huchenlei@proton.me>

test/__snapshots__/litegraph.test.ts.snap

@@ -55,6 +55,7 @@ LiteGraphGlobal {
   "NODE_DEFAULT_BOXCOLOR": "#666",
   "NODE_DEFAULT_COLOR": "#333",
   "NODE_DEFAULT_SHAPE": "box",
+  "NODE_ERROR_COLOUR": "#E00",
   "NODE_MIN_WIDTH": 50,
   "NODE_MODES": [
     "Always",
@@ -175,6 +176,7 @@ LiteGraphGlobal {
   "snap_highlights_node": true,
   "snaps_for_comfy": true,
   "throw_errors": true,
+  "use_legacy_node_error_indicator": false,
   "use_uuids": false,
 }
 `;