chore: Make terminal_view own the TerminalSlashCommand (#31070)

This reduces 'touch crates/editor/src/editor.rs && cargo +nightly build'
from 8.9s to 8.5s. That same scenario used to take 8s less than a week
ago. :)
I'm measuring with nightly rustc, because it's compile times are better
than those of stable thanks to
https://github.com/rust-lang/rust/pull/138522

main (8.2s total):

![image](https://github.com/user-attachments/assets/767a2ac4-7bba-4147-bd16-9b09eed5b433)

[cargo-timing.html.zip](https://github.com/user-attachments/files/20364175/cargo-timing.html.zip)

#22be776 (7.5s total):

[cargo-timing-20250521T085303.892834Z.html.zip](https://github.com/user-attachments/files/20364391/cargo-timing-20250521T085303.892834Z.html.zip)

![image](https://github.com/user-attachments/assets/c4476df9-cb6e-4403-b0db-de00521f1fd0)


Release Notes:

- N/A

crates/agent/src/agent.rs

@@ -217,7 +217,6 @@ fn register_slash_commands(cx: &mut App) {
     slash_command_registry.register_command(assistant_slash_commands::PromptSlashCommand, true);
     slash_command_registry.register_command(assistant_slash_commands::SelectionCommand, true);
     slash_command_registry.register_command(assistant_slash_commands::DefaultSlashCommand, false);
-    slash_command_registry.register_command(assistant_slash_commands::TerminalSlashCommand, true);
     slash_command_registry.register_command(assistant_slash_commands::NowSlashCommand, false);
     slash_command_registry
         .register_command(assistant_slash_commands::DiagnosticsSlashCommand, true);

crates/agent/src/agent_model_selector.rs

@@ -3,10 +3,10 @@ use fs::Fs;
 use gpui::{Entity, FocusHandle, SharedString};
 
 use crate::Thread;
-use language_model::{ConfiguredModel, LanguageModelRegistry};
-use language_model_selector::{
+use assistant_context_editor::language_model_selector::{
     LanguageModelSelector, LanguageModelSelectorPopoverMenu, ToggleModelSelector,
 };
+use language_model::{ConfiguredModel, LanguageModelRegistry};
 use settings::update_settings_file;
 use std::sync::Arc;
 use ui::{PopoverMenuHandle, Tooltip, prelude::*};

crates/agent/src/agent_panel.rs

@@ -17,6 +17,7 @@ use assistant_settings::{AssistantDockPosition, AssistantSettings};
 use assistant_slash_command::SlashCommandWorkingSet;
 use assistant_tool::ToolWorkingSet;
 
+use assistant_context_editor::language_model_selector::ToggleModelSelector;
 use client::{UserStore, zed_urls};
 use editor::{Anchor, AnchorRangeExt as _, Editor, EditorEvent, MultiBuffer};
 use fs::Fs;
@@ -30,7 +31,6 @@ use language::LanguageRegistry;
 use language_model::{
     LanguageModelProviderTosView, LanguageModelRegistry, RequestUsage, ZED_CLOUD_PROVIDER_ID,
 };
-use language_model_selector::ToggleModelSelector;
 use project::{Project, ProjectPath, Worktree};
 use prompt_store::{PromptBuilder, PromptStore, UserPromptId};
 use proto::Plan;

crates/agent/src/inline_prompt_editor.rs

@@ -9,6 +9,7 @@ use crate::terminal_codegen::TerminalCodegen;
 use crate::thread_store::{TextThreadStore, ThreadStore};
 use crate::{CycleNextInlineAssist, CyclePreviousInlineAssist};
 use crate::{RemoveAllContext, ToggleContextPicker};
+use assistant_context_editor::language_model_selector::ToggleModelSelector;
 use client::ErrorExt;
 use collections::VecDeque;
 use db::kvp::Dismissable;
@@ -24,7 +25,6 @@ use gpui::{
     Focusable, FontWeight, Subscription, TextStyle, WeakEntity, Window, anchored, deferred, point,
 };
 use language_model::{LanguageModel, LanguageModelRegistry};
-use language_model_selector::ToggleModelSelector;
 use parking_lot::Mutex;
 use settings::Settings;
 use std::cmp;

crates/agent/src/message_editor.rs

@@ -8,6 +8,7 @@ use crate::ui::{
     AnimatedLabel, MaxModeTooltip,
     preview::{AgentPreview, UsageCallout},
 };
+use assistant_context_editor::language_model_selector::ToggleModelSelector;
 use assistant_settings::{AssistantSettings, CompletionMode};
 use buffer_diff::BufferDiff;
 use client::UserStore;
@@ -30,7 +31,6 @@ use language_model::{
     ConfiguredModel, LanguageModelRequestMessage, MessageContent, RequestUsage,
     ZED_CLOUD_PROVIDER_ID,
 };
-use language_model_selector::ToggleModelSelector;
 use multi_buffer;
 use project::Project;
 use prompt_store::PromptStore;