Add "Fix with Assistant" code action on lines with diagnostics (#18163)

Release Notes:

- Added a new "Fix with Assistant" action on code with errors or
warnings.

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Co-authored-by: Nathan <nathan@zed.dev>

crates/assistant/Cargo.toml

@@ -51,6 +51,7 @@ indoc.workspace = true
 language.workspace = true
 language_model.workspace = true
 log.workspace = true
+lsp.workspace = true
 markdown.workspace = true
 menu.workspace = true
 multi_buffer.workspace = true