docs(core): add JSDoc for getId

packages/sanity/src/core/form/store/utils/getId.ts

@@ -4,6 +4,19 @@ const idCache = new WeakMap<object, string>()
 const undefinedKey = Symbol('GetIdUndefined')
 const nullKey = Symbol('GetIdNull')
 
+/**
+ * Generates a stable ID for various types of values, including `undefined`, `null`, objects, functions, and symbols.
+ *
+ * - **Primitives (string, number, boolean):** The value itself is used as the ID.
+ * - **Undefined and null:** Special symbols (`undefinedKey` and `nullKey`) are used to generate unique IDs.
+ * - **Objects and functions:** An ID is generated using the `nanoid` library and cached in a `WeakMap` for stable future retrieval.
+ *
+ * This function is used to reconcile inputs in `prepareFormState` immutably, allowing IDs to be generated and cached based
+ * on the reference of the object. This ensures that memoization functions can use these IDs for consistent hashing without
+ * recalculating on each call, as the inputs themselves are immutably edited.
+ *
+ * @internal
+ */
 export function getId(value: unknown): string {
   switch (typeof value) {
     case 'undefined': {