multiple: enforce standards on tool_choice (#30372)

- Test if models support forcing tool calls via `tool_choice`. If they
do, they should support
  - `"any"` to specify any tool
  - the tool name as a string to force calling a particular tool
- Add `tool_choice` to signature of `BaseChatModel.bind_tools` in core
- Deprecate `tool_choice_value` in standard tests in favor of a boolean
`has_tool_choice`

Will follow up with PRs in external repos (tested in AWS and Google
already).

libs/standard-tests/langchain_tests/unit_tests/chat_models.py

@@ -2,6 +2,7 @@
 :autodoc-options: autoproperty
 """
 
+import inspect
 import os
 from abc import abstractmethod
 from typing import Any, Dict, List, Literal, Optional, Tuple, Type
@@ -127,6 +128,14 @@ class ChatModelTests(BaseStandardTests):
         """(None or str) to use for tool choice when used in tests."""
         return None
 
+    @property
+    def has_tool_choice(self) -> bool:
+        """(bool) whether the model supports tool calling."""
+        bind_tools_params = inspect.signature(
+            self.chat_model_class.bind_tools
+        ).parameters
+        return "tool_choice" in bind_tools_params
+
     @property
     def has_structured_output(self) -> bool:
         """(bool) whether the chat model supports structured output."""
@@ -273,12 +282,11 @@ class ChatModelUnitTests(ChatModelTests):
 
         Value to use for tool choice when used in tests.
 
-        Some tests for tool calling features attempt to force tool calling via a
-        `tool_choice` parameter. A common value for this parameter is "any". Defaults
-        to `None`.
-
-        Note: if the value is set to "tool_name", the name of the tool used in each
-        test will be set as the value for `tool_choice`.
+        .. warning:: Deprecated since version 0.3.15:
+           This property will be removed in version 0.3.20. If a model does not
+           support forcing tool calling, override the ``has_tool_choice`` property to
+           return ``False``. Otherwise, models should accept values of ``"any"`` or
+           the name of a tool in ``tool_choice``.
 
         Example:
 
@@ -288,6 +296,26 @@ class ChatModelUnitTests(ChatModelTests):
             def tool_choice_value(self) -> Optional[str]:
                 return "any"
 
+    .. dropdown:: has_tool_choice
+
+        Boolean property indicating whether the chat model supports forcing tool
+        calling via a ``tool_choice`` parameter.
+
+        By default, this is determined by whether the parameter is included in the
+        signature for the corresponding ``bind_tools`` method.
+
+        If ``True``, the minimum requirement for this feature is that
+        ``tool_choice="any"`` will force a tool call, and ``tool_choice=<tool name>``
+        will force a call to a specific tool.
+
+        Example override:
+
+        .. code-block:: python
+
+            @property
+            def has_tool_choice(self) -> bool:
+                return False
+
     .. dropdown:: has_structured_output
 
         Boolean property indicating whether the chat model supports structured