gpui: Don't export named Context from prelude (#21869)

This PR updates the `gpui::prelude` to not export the `Context` trait
named.

This prevents some naming clashes in downstream consumers.

Release Notes:

- N/A

crates/copilot/src/copilot_chat.rs

@@ -6,13 +6,12 @@ use anyhow::{anyhow, Result};
 use chrono::DateTime;
 use fs::Fs;
 use futures::{io::BufReader, stream::BoxStream, AsyncBufReadExt, AsyncReadExt, StreamExt};
-use gpui::{AppContext, AsyncAppContext, Global};
+use gpui::{prelude::*, AppContext, AsyncAppContext, Global};
 use http_client::{AsyncBody, HttpClient, Method, Request as HttpRequest};
 use paths::home_dir;
 use serde::{Deserialize, Serialize};
 use settings::watch_config_file;
 use strum::EnumIter;
-use ui::Context;
 
 pub const COPILOT_CHAT_COMPLETION_URL: &str = "https://api.githubcopilot.com/chat/completions";
 pub const COPILOT_CHAT_AUTH_URL: &str = "https://api.github.com/copilot_internal/v2/token";