Add Create Directory Tool (#27505)

`mkdir -p` but it works cross-platform and uses project abstractions.

<img width="629" alt="Screenshot 2025-03-26 at 11 02 37 AM"
src="https://github.com/user-attachments/assets/9ef58d53-3343-4c94-a8f3-b82ab942611b"
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Release Notes:

- N/A

crates/assistant_tools/src/create_directory_tool/description.md

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+Creates a new directory at the specified path within the project. Returns confirmation that the directory was created.
+
+This tool creates a directory and all necessary parent directories (similar to `mkdir -p`). It should be used whenever you need to create new directories within the project.