Add LLM for Alibaba's Damo Academy's Tongyi Qwen API (#7477)

- Add langchain.llms.Tonyi for text completion, in examples into the
Tonyi Text API,
- Add system tests.

Note async completion for the Text API is not yet supported and will be
included in a future PR.

Dependencies: dashscope. It will be installed manually cause it is not
need by everyone.

Happy for feedback on any aspect of this PR @hwchase17 @baskaryan.

tests/integration_tests/llms/test_tongyi.py

@@ -0,0 +1,27 @@
+"""Test Tongyi API wrapper."""
+from langchain.llms.tongyi import Tongyi
+from langchain.schema import LLMResult
+
+
+def test_tongyi_call() -> None:
+    """Test valid call to tongyi."""
+    llm = Tongyi()
+    output = llm("who are you")
+    assert isinstance(output, str)
+
+
+def test_tongyi_generate() -> None:
+    """Test valid call to tongyi."""
+    llm = Tongyi()
+    output = llm.generate(["who are you"])
+    assert isinstance(output, LLMResult)
+    assert isinstance(output.generations, list)
+
+
+def test_tongyi_generate_stream() -> None:
+    """Test valid call to tongyi."""
+    llm = Tongyi(streaming=True)
+    output = llm.generate(["who are you"])
+    print(output)
+    assert isinstance(output, LLMResult)
+    assert isinstance(output.generations, list)