Pass up intent with completion requests (#31710)

This PR adds a new `intent` field to completion requests to assist in
categorizing them correctly.

Release Notes:

- N/A

---------

Co-authored-by: Ben Brandt <benjamin.j.brandt@gmail.com>

crates/eval/Cargo.toml

@@ -67,3 +67,4 @@ unindent.workspace = true
 util.workspace = true
 uuid.workspace = true
 workspace-hack.workspace = true
+zed_llm_client.workspace = true