docs(bedrock-agent-function): extract inline code examples into snippet files

Extract 14 inline C# code blocks from
docs/core/event_handler/bedrock_agent_function.md into standalone snippet files
under docs/snippets/bedrock-agent-function/ using pymdownx.snippets includes.
No visual changes to rendered documentation.

Closes #1186
Refs #794, #1104

Author: hjgraca