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/terminal_view/src/terminal_view.rs

@@ -2,8 +2,10 @@ mod persistence;
 pub mod terminal_element;
 pub mod terminal_panel;
 pub mod terminal_scrollbar;
+mod terminal_slash_command;
 pub mod terminal_tab_tooltip;
 
+use assistant_slash_command::SlashCommandRegistry;
 use editor::{Editor, EditorSettings, actions::SelectAll, scroll::ScrollbarAutoHide};
 use gpui::{
     AnyElement, App, DismissEvent, Entity, EventEmitter, FocusHandle, Focusable, KeyContext,
@@ -29,6 +31,7 @@ use terminal::{
 use terminal_element::{TerminalElement, is_blank};
 use terminal_panel::TerminalPanel;
 use terminal_scrollbar::TerminalScrollHandle;
+use terminal_slash_command::TerminalSlashCommand;
 use terminal_tab_tooltip::TerminalTooltip;
 use ui::{
     ContextMenu, Icon, IconName, Label, Scrollbar, ScrollbarState, Tooltip, h_flex, prelude::*,
@@ -78,6 +81,7 @@ actions!(terminal, [RerunTask]);
 impl_actions!(terminal, [SendText, SendKeystroke]);
 
 pub fn init(cx: &mut App) {
+    assistant_slash_command::init(cx);
     terminal_panel::init(cx);
     terminal::init(cx);
 
@@ -87,6 +91,7 @@ pub fn init(cx: &mut App) {
         workspace.register_action(TerminalView::deploy);
     })
     .detach();
+    SlashCommandRegistry::global(cx).register_command(TerminalSlashCommand, true);
 }
 
 pub struct BlockProperties {