Add chat_coder.py to enable chat-based coding assistance.

aider/coders/chat_coder.py

@@ -0,0 +1,19 @@
+from pathlib import Path
+
+from aider import diffs
+
+from ..dump import dump  # noqa: F401
+from .base_coder import Coder
+from .chat_prompts import ChatPrompts
+
+
+class ChatCoder(Coder):
+    edit_format = "chat"
+
+    gpt_prompts = ChatPrompts()
+
+    def get_edits(self, mode="update"):
+        return
+
+    def apply_edits(self, edits):
+        return