Add staged status information to diff hunks (#24475)

Release Notes:

- Render unstaged hunks in the project diff editor with a slashed
background

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Co-authored-by: maxbrunsfeld <max@zed.dev>
Co-authored-by: Max Brunsfeld <maxbrunsfeld@gmail.com>

crates/project/src/project.rs

@@ -21,7 +21,7 @@ mod project_tests;
 
 mod direnv;
 mod environment;
-use diff::BufferDiff;
+use buffer_diff::BufferDiff;
 pub use environment::EnvironmentErrorMessage;
 use git::Repository;
 pub mod search_history;