Use line-based and word-based diff when reloading and formatting buffers (#25129)

Closes https://github.com/zed-industries/zed/issues/10122
Closes https://github.com/zed-industries/zed/issues/25034

When formatting buffers or reloading them after they change on disk, we
performed a diff between the buffer's current contents and the new
content. We need this diff in order preserve the positions of cursors
and other decorations when updating the buffer's text.

In order to handle changes within lines, we would previously compute a
*character-wise* diff. This was extremely expensive for large files.

This PR gets rid of the character-wise diff, and instead performs a
normal line-wise diff. Then, for certain replace hunks, we compute a
secondary word-based diff. Also, I've switched to the
[`imara-diff`](https://github.com/pascalkuthe/imara-diff) crate, instead
of `similar`.

Release Notes:

- Fixed a hang that could occur when large files were changed on disk or
formatted.

crates/language/src/language.rs

@@ -15,6 +15,7 @@ mod outline;
 pub mod proto;
 mod syntax_map;
 mod task_context;
+mod text_diff;
 mod toolchain;
 
 #[cfg(test)]
@@ -62,6 +63,7 @@ use std::{num::NonZeroU32, sync::OnceLock};
 use syntax_map::{QueryCursorHandle, SyntaxSnapshot};
 use task::RunnableTag;
 pub use task_context::{ContextProvider, RunnableRange};
+pub use text_diff::{line_diff, text_diff, text_diff_with_options, unified_diff, DiffOptions};
 use theme::SyntaxTheme;
 pub use toolchain::{LanguageToolchainStore, Toolchain, ToolchainList, ToolchainLister};
 use tree_sitter::{self, wasmtime, Query, QueryCursor, WasmStore};