Extract an agent_ui crate from agent (#33284)

This PR moves the UI-dependent logic in the `agent` crate into its own
crate, `agent_ui`. The remaining `agent` crate no longer depends on
`editor`, `picker`, `ui`, `workspace`, etc.

This has compile time benefits, but the main motivation is to isolate
our core agentic logic, so that we can make agents more
pluggable/configurable.

Release Notes:

- N/A

crates/agent/src/tool_use.rs

@@ -1,24 +1,23 @@
-use std::sync::Arc;
-
+use crate::{
+    thread::{MessageId, PromptId, ThreadId},
+    thread_store::SerializedMessage,
+};
 use anyhow::Result;
 use assistant_tool::{
     AnyToolCard, Tool, ToolResultContent, ToolResultOutput, ToolUseStatus, ToolWorkingSet,
 };
 use collections::HashMap;
-use futures::FutureExt as _;
-use futures::future::Shared;
-use gpui::{App, Entity, SharedString, Task};
+use futures::{FutureExt as _, future::Shared};
+use gpui::{App, Entity, SharedString, Task, Window};
+use icons::IconName;
 use language_model::{
     ConfiguredModel, LanguageModel, LanguageModelRequest, LanguageModelToolResult,
     LanguageModelToolResultContent, LanguageModelToolUse, LanguageModelToolUseId, Role,
 };
 use project::Project;
-use ui::{IconName, Window};
+use std::sync::Arc;
 use util::truncate_lines_to_byte_limit;
 
-use crate::thread::{MessageId, PromptId, ThreadId};
-use crate::thread_store::SerializedMessage;
-
 #[derive(Debug)]
 pub struct ToolUse {
     pub id: LanguageModelToolUseId,
@@ -26,7 +25,7 @@ pub struct ToolUse {
     pub ui_text: SharedString,
     pub status: ToolUseStatus,
     pub input: serde_json::Value,
-    pub icon: ui::IconName,
+    pub icon: icons::IconName,
     pub needs_confirmation: bool,
 }