Add Code Symbols tool (#27733)

Lets you get all the code symbols in the project (like the Code Symbols
panel) or in a particular file (like the Outline panel), optionally
paginated and filtering results by regex. The tool gives the files,
lines, and numbers of all of these, which means they can be used in
conjunction with the read file tool to read subsets of large files
without having to open the entire large file and poke around in it.

<img width="621" alt="Screenshot 2025-03-29 at 12 00 21 PM"
src="https://github.com/user-attachments/assets/d78259d7-2746-44c0-ac18-2e21f2505c0a"
/>

Release Notes:

- N/A

crates/assistant_tools/Cargo.toml

@@ -25,7 +25,10 @@ http_client.workspace = true
 itertools.workspace = true
 language.workspace = true
 language_model.workspace = true
+log.workspace = true
+lsp.workspace = true
 project.workspace = true
+regex.workspace = true
 release_channel.workspace = true
 schemars.workspace = true
 serde.workspace = true