feat: add XML tool call fallback for OpenAI-compatible providers

Some API providers (like kie.ai with Gemini 3 Pro) do not fully support
native function calling and instead output XML-formatted tool calls in
text responses. This change adds support for parsing these XML tool calls
and executing them as a fallback.

Changes:
- Add XmlToolCallParser to parse XML tool calls from text content
- Modify presentAssistantMessage to detect and parse XML tool calls
  instead of rejecting them with an error
- Add comprehensive tests for the XmlToolCallParser

Fixes #11011

Author: roomote