Display-only ACP terminals (#39419)

Codex needs (and future projects are anticipated to need as well) a
concept of display-only terminals. This refactors terminals to decouple
the PTY part from the display part, so that we can render terminal
changes based on a series of events - regardless of whether they're
being driven from a PTY inside Zed or from an outside source (e.g.
`codex-acp`).

Release Notes:

- N/A

Cargo.lock

@@ -318,9 +318,11 @@ dependencies = [
  "smol",
  "task",
  "tempfile",
+ "terminal",
  "thiserror 2.0.12",
  "ui",
  "util",
+ "uuid",
  "watch",
  "workspace-hack",
 ]