[Refactor] Split NodeSlot out to separate files (#960)

Split files only; no code changes.  New files moved to `/node`.

src/node/NodeInputSlot.ts

@@ -0,0 +1,40 @@
+import type { INodeInputSlot, INodeOutputSlot, OptionalProps } from "@/interfaces"
+import type { LinkId } from "@/LLink"
+
+import { LabelPosition } from "@/draw"
+import { LiteGraph } from "@/litegraph"
+import { type IDrawOptions, NodeSlot } from "@/node/NodeSlot"
+
+export class NodeInputSlot extends NodeSlot implements INodeInputSlot {
+  link: LinkId | null
+
+  get isWidgetInputSlot(): boolean {
+    return !!this.widget
+  }
+
+  constructor(slot: OptionalProps<INodeInputSlot, "boundingRect">) {
+    super(slot)
+    this.link = slot.link
+  }
+
+  override isConnected(): boolean {
+    return this.link != null
+  }
+
+  override isValidTarget(fromSlot: INodeInputSlot | INodeOutputSlot): boolean {
+    return "links" in fromSlot && LiteGraph.isValidConnection(this.type, fromSlot.type)
+  }
+
+  override draw(ctx: CanvasRenderingContext2D, options: Omit<IDrawOptions, "doStroke" | "labelPosition">) {
+    const originalTextAlign = ctx.textAlign
+    ctx.textAlign = "left"
+
+    super.draw(ctx, {
+      ...options,
+      labelPosition: LabelPosition.Right,
+      doStroke: false,
+    })
+
+    ctx.textAlign = originalTextAlign
+  }
+}