AK/LibAudio: Add stream read operators to AK::BufferStream, and use it in AWavLoader

At the same time, we allow chaining of streaming operators, and add a
way to check for partial reads (also used in WAV parsing).

Libraries/LibAudio/AWavLoader.h

@@ -9,6 +9,6 @@ public:
     RefPtr<AWavFile> load_wav(const StringView& path);
     const char* error_string() { return m_error_string.characters(); }
 private:
-    RefPtr<AWavFile> parse_wav(const ByteBuffer& buffer);
+    RefPtr<AWavFile> parse_wav(ByteBuffer& buffer);
     String m_error_string;
 };