[llvm] [ADT] Adding bidirectional iterator functionality + unit tests (PR #160726)

[Jakub Kuderski via llvm-commits]

================
@@ -1177,6 +1178,98 @@ TYPED_TEST(BitVectorTest, Iterators) {
     EXPECT_EQ(List[i++], Bit);
 }
 
+TYPED_TEST(BitVectorTest, BidirectionalIterator) {
+  // Test decrement operators
+  TypeParam Vec(100, false);
+  Vec.set(10);
+  Vec.set(20);
+  Vec.set(30);
+  Vec.set(40);
+
+  // Test that we can decrement from end()
----------------
kuhar wrote:

```suggestion
  // Test that we can decrement from end().
```

https://github.com/llvm/llvm-project/pull/160726