[clang] [NFC] [Serializer] Pack information in serializer (PR #69287)

[Vassil Vassilev via cfe-commits]

================
@@ -2407,6 +2407,53 @@ class ASTReader
   bool isProcessingUpdateRecords() { return ProcessingUpdateRecords; }
 };
 
+/// A simple helper class to unpack an integer to bits and consuming
+/// the bits in order.
+class BitsUnpacker {
+  constexpr static uint32_t BitsIndexUpbound = 32;
+
+public:
+  BitsUnpacker(uint32_t V) { updateValue(V); }
+  BitsUnpacker(const BitsUnpacker &) = delete;
+  BitsUnpacker(BitsUnpacker &&) = delete;
+  BitsUnpacker operator=(const BitsUnpacker &) = delete;
+  BitsUnpacker operator=(BitsUnpacker &&) = delete;
+  ~BitsUnpacker() {
+#ifndef NDEBUG
+    while (isValid())
+      assert(!getNextBit() && "There are bits failed to read!");
----------------
vgvassilev wrote:

```suggestion
      assert(!getNextBit() && "There are unprocessed bits!");
```

Is that the analog of `hasUnconsumedValues`? If so, we could probably mirror it here, too.

https://github.com/llvm/llvm-project/pull/69287