[rest] fix aiohttp read in rest (#20952)

Author: iscai-msft

sdk/core/azure-core/CHANGELOG.md

@@ -1,6 +1,6 @@
 # Release History
 
-## 1.19.0 (Unreleased)
+## 1.19.0 (2021-09-30)
 
 ### Features Added
 

sdk/core/azure-core/azure/core/rest/_aiohttp.py

@@ -171,6 +171,18 @@ def __getstate__(self):
         state['headers'] = CIMultiDict(self.headers)  # MultiDictProxy is not pickable
         return state
 
+    async def read(self) -> bytes:
+        """Read the response's bytes into memory.
+
+        :return: The response's bytes
+        :rtype: bytes
+        """
+        if not self._content:
+            self._stream_download_check()
+            self._content = await self._internal_response.read()
+        await self._set_read_checks()
+        return _aiohttp_body_helper(self)
+
     async def close(self) -> None:
         """Close the response.