acp: Add a basic test for ACP remoting (#38381)

Tests that the downstream project can see custom agents configured in
the remote server's settings, and that it constructs an appropriate
`AgentServerCommand`.

Release Notes:

- N/A

Cargo.lock

@@ -13981,6 +13981,7 @@ dependencies = [
  "clap",
  "client",
  "clock",
+ "collections",
  "crash-handler",
  "crashes",
  "dap",
@@ -14009,6 +14010,7 @@ dependencies = [
  "minidumper",
  "node_runtime",
  "paths",
+ "pretty_assertions",
  "project",
  "proto",
  "release_channel",