[BUGFIX 3.12] Backport Symbol fix (#6416)

* Add a Symbol-like symbol (thank you glimmer-vm)

This is similar to what is implemented here:
https://github.com/glimmerjs/glimmer-vm/blob/72718d0d6ebb2614ec984f51435a44830d410e4c/packages/%40glimmer/reference/lib/validators.ts

* Replace `Symbol`s that may be iterable by `symbol`s

These occurences of Symbol might be replaced by this `symbol`, similar
but different in the sense it is iterable.

packages/store/addon/-private/ts-interfaces/utils/brand.ts

@@ -1,3 +1,5 @@
+import { symbol } from './symbol';
+
 /**
   @module @ember-data/store
 */
@@ -14,4 +16,5 @@
  *
  * @internal
  */
-export const BRAND_SYMBOL = Symbol(`DEBUG-ts-brand`);
+
+export const BRAND_SYMBOL: unique symbol = symbol('DEBUG-ts-brand');

packages/store/addon/-private/ts-interfaces/utils/symbol.ts

@@ -0,0 +1,19 @@
+/**
+  @module @ember-data/store
+*/
+
+/**
+ * This symbol provides a Symbol replacement for browsers that do not have it
+ * (eg. IE 11).
+ *
+ * The replacement is different from the native Symbol in some ways. It is a
+ * function that produces an output:
+ * - iterable;
+ * - that is a string, not a symbol.
+ *
+ * @internal
+ */
+export const symbol =
+  typeof Symbol !== 'undefined'
+    ? Symbol
+    : (key: string) => `__${key}${Math.floor(Math.random() * Date.now())}__` as any;