Restructure workflow step resolution and fix inserting newlines (#15720)

Release Notes:

- N/A

---------

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

crates/assistant/Cargo.toml

@@ -67,7 +67,6 @@ serde_json.workspace = true
 settings.workspace = true
 similar.workspace = true
 smol.workspace = true
-strsim.workspace = true
 telemetry_events.workspace = true
 terminal.workspace = true
 terminal_view.workspace = true
@@ -86,6 +85,7 @@ ctor.workspace = true
 editor = { workspace = true, features = ["test-support"] }
 env_logger.workspace = true
 language = { workspace = true, features = ["test-support"] }
+language_model = { workspace = true, features = ["test-support"] }
 log.workspace = true
 project = { workspace = true, features = ["test-support"] }
 rand.workspace = true