assistant_tools: Rename `RegexSearchTool` module to match the others (#27001)

This PR renames the `RegexSearchTool` module to `regex_search_tool.rs`
to match the other tools.

Release Notes:

- N/A
b70f21c08dMarshall Bowers committed on 3/18/2025, 4:20:15 PM· committed by GitHubparent5615be5
3 files changedLine totals unavailable