Fix unnecessarily large edits emitted from multi buffer on diff recalculation (#23753)

This fixes an issue introduced in #22994 where soft wrap would
recalculate for the entire buffer when editing.

Release Notes:

- N/A

---------

Co-authored-by: Conrad <conrad@zed.dev>

crates/text/Cargo.toml

@@ -13,7 +13,7 @@ path = "src/text.rs"
 doctest = false
 
 [features]
-test-support = ["rand"]
+test-support = ["rand", "util/test-support"]
 
 [dependencies]
 anyhow.workspace = true