Remove FunctionGemma and restore XML toolcall infrastructure
- Remove function_gemma parser, mapper, template, and tests
- Restore chat-parser-xml-toolcall.cpp/.h from master
- Add missing method declarations to chat-parser.h
- Add missing functional mapper declarations to chat-peg-parser.h
- Fix mapper function naming (_func suffix) in chat-parser.cpp
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Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>
