[API] Add improved slot locator functions (#716)

- Returns object with slot, index, and pos
- Locate-by-type returns object with slot & index
- Uses standard `undefined` return for concise chaining & validation
- Free 10x perf increase over getConnectionPos (used basic random data
to test, out of curiosity)

src/interfaces.ts

@@ -217,6 +217,11 @@ export interface IOptionalSlotData<TSlot extends INodeInputSlot | INodeOutputSlo
   className?: string
 }
 
+/**
+ * A string that represents a specific data / slot type, e.g. `STRING`.
+ *
+ * Can be comma-delimited to specify multiple allowed types, e.g. `STRING,INT`.
+ */
 export type ISlotType = number | string
 
 export interface INodeSlot {