[PM-7289] implement generator libraries (#9549)

This is a copy of the files. The source in `@bitwarden/common` will be deleted once
all of the applications have been ported to the library.

libs/common/src/tools/rx.ts

@@ -0,0 +1,38 @@
+import { map, distinctUntilChanged, OperatorFunction } from "rxjs";
+
+/**
+ * An observable operator that reduces an emitted collection to a single object,
+ * returning a default if all items are ignored.
+ * @param reduce The reduce function to apply to the filtered collection. The
+ *  first argument is the accumulator, and the second is the current item. The
+ *  return value is the new accumulator.
+ * @param defaultValue The default value to return if the collection is empty. The
+ *   default value is also the initial value of the accumulator.
+ */
+export function reduceCollection<Item, Accumulator>(
+  reduce: (acc: Accumulator, value: Item) => Accumulator,
+  defaultValue: Accumulator,
+): OperatorFunction<Item[], Accumulator> {
+  return map((values: Item[]) => {
+    const reduced = (values ?? []).reduce(reduce, structuredClone(defaultValue));
+    return reduced;
+  });
+}
+
+/**
+ * An observable operator that emits distinct values by checking that all
+ *   values in the previous entry match the next entry. This method emits
+ *   when a key is added and does not when a key is removed.
+ * @remarks This method checks objects. It does not check items in arrays.
+ */
+export function distinctIfShallowMatch<Item>(): OperatorFunction<Item, Item> {
+  return distinctUntilChanged((previous, current) => {
+    let isDistinct = true;
+
+    for (const key in current) {
+      isDistinct &&= previous[key] === current[key];
+    }
+
+    return isDistinct;
+  });
+}