Python: Fix agent group chat bug related to function calling in ChatCompletionAgent

[moonbox3]

Motivation and Context

During a group chat, if using an OpenAIAssistantAgent, the addition of a ChatCompletionMessage to the AssistantAgent channel was breaking because we were including FunctionCallContent. Additionally, there needs to be some translation of a FunctionResultContent type to a text type when adding a ChatCompletionAgent message to an AssistantAgent thread message. The AuthorRole can only be 'user' or 'assistant'.

Description

Fixes for the items mentioned above. This may not be a perfect solution, but getting this in and I can revisit it to align more closely with how dotnet handles the FunctionResultContent/TextContent as part of the overall ChatMessageContent.

• This PR also adds a new sample showing mixed agent chat and a ChatCompletionAgent using plugins.

Contribution Checklist

• The code builds clean without any errors or warnings
• The PR follows the SK Contribution Guidelines and the pre-submission formatting script raises no violations
• All unit tests pass, and I have added new tests where possible
• I didn't break anyone 😄

[markwallace-microsoft]

Python Test Coverage Report

File	Stmts	Miss	Cover	Missing
semantic_kernel
kernel.py	199	47	76%	150, 161, 165, 315–318, 425, 439–482
semantic_kernel/agents/channels
open_ai_assistant_channel.py	49	1	98%	42
semantic_kernel/agents/group_chat
agent_chat.py	116	1	99%	91
agent_group_chat.py	67	2	97%	113, 135
broadcast_queue.py	72	1	99%	35
semantic_kernel/agents/open_ai
assistant_content_generation.py	68	2	97%	81–82
open_ai_assistant_base.py	361	3	99%	243, 321–322
semantic_kernel/connectors/ai/anthropic/services
anthropic_chat_completion.py	94	25	73%	171–181, 196–205, 222–236
semantic_kernel/connectors/ai/azure_ai_inference/services
azure_ai_inference_chat_completion.py	150	4	97%	174, 324–325, 441
semantic_kernel/connectors/ai/embeddings
embedding_generator_base.py	8	1	88%	50
semantic_kernel/connectors/ai/google
shared_utils.py	39	2	95%	97, 119
semantic_kernel/connectors/ai/google/google_ai/services
google_ai_chat_completion.py	150	4	97%	153, 265, 299–300
utils.py	63	3	95%	139, 157–162
semantic_kernel/connectors/ai/google/vertex_ai/services
utils.py	65	3	95%	141, 159–164
vertex_ai_chat_completion.py	150	4	97%	147, 258, 292–293
semantic_kernel/connectors/ai/hugging_face/services
hf_text_completion.py	54	3	94%	97, 105, 136
hf_text_embedding.py	32	5	84%	79–83
semantic_kernel/connectors/memory/azure_ai_search
azure_ai_search_collection.py	87	2	98%	150, 152
semantic_kernel/connectors/memory/redis
redis_collection.py	160	2	99%	146, 316
utils.py	45	11	76%	145–146, 164, 166, 173–188
semantic_kernel/connectors/openapi_plugin
openapi_manager.py	58	2	97%	110–111
openapi_parser.py	88	1	99%	127
openapi_runner.py	105	2	98%	181–182
semantic_kernel/connectors/openapi_plugin/models
rest_api_operation.py	129	1	99%	242
semantic_kernel/contents
function_call_content.py	97	1	99%	201
semantic_kernel/data
vector_store_record_collection.py	249	19	92%	410, 470–474, 482–486, 526–529, 536–539
vector_store_record_utils.py	26	2	92%	50, 52
semantic_kernel/functions
kernel_function_decorator.py	98	1	99%	102
kernel_function_from_method.py	96	1	99%	153
kernel_function_from_prompt.py	154	7	95%	165–166, 180, 201, 219, 239, 322
kernel_function_log_messages.py	33	2	94%	36–37
kernel_plugin.py	187	2	99%	472, 475
semantic_kernel/planners
plan.py	234	45	81%	54, 163–165, 197, 214–227, 264, 269, 277–278, 288–291, 308, 313, 329, 332–337, 355, 360, 363, 365, 372, 386–388, 393–397
semantic_kernel/planners/function_calling_stepwise_planner
function_calling_stepwise_planner.py	116	4	97%	145, 189–190, 198
semantic_kernel/planners/sequential_planner
sequential_planner.py	64	6	91%	71, 75, 109, 125, 134–135
sequential_planner_extensions.py	50	9	82%	31–32, 56, 110–124
sequential_planner_parser.py	77	12	84%	66–74, 93, 117–120
semantic_kernel/schema
kernel_json_schema_builder.py	119	5	96%	50, 84, 206, 210–211
semantic_kernel/template_engine/blocks
code_block.py	77	1	99%	119
named_arg_block.py	43	1	98%	98
semantic_kernel/utils/telemetry
decorators.py	113	4	96%	232, 240, 243, 252
user_agent.py	16	2	88%	18–19
TOTAL	10767	256	98%

Python Unit Test Overview

Tests	Skipped	Failures	Errors	Time
2370	1 💤	0 ❌	0 🔥	52.072s ⏱️