Add a SlashCommandResult type alias (#19633)

This PR adds a new `SlashCommandResult` type alias.

We're going to be changing what slash commands can return in order to
support streaming, so having this type alias in place will make that
switch a bit more neat.

Release Notes:

- N/A

crates/assistant/src/slash_command/workflow_command.rs

@@ -1,18 +1,18 @@
-use crate::prompts::PromptBuilder;
-use std::sync::Arc;
-
 use std::sync::atomic::AtomicBool;
+use std::sync::Arc;
 
 use anyhow::Result;
 use assistant_slash_command::{
     ArgumentCompletion, SlashCommand, SlashCommandOutput, SlashCommandOutputSection,
+    SlashCommandResult,
 };
 use gpui::{Task, WeakView};
 use language::{BufferSnapshot, LspAdapterDelegate};
 use ui::prelude::*;
-
 use workspace::Workspace;
 
+use crate::prompts::PromptBuilder;
+
 pub(crate) struct WorkflowSlashCommand {
     prompt_builder: Arc<PromptBuilder>,
 }
@@ -60,7 +60,7 @@ impl SlashCommand for WorkflowSlashCommand {
         _workspace: WeakView<Workspace>,
         _delegate: Option<Arc<dyn LspAdapterDelegate>>,
         cx: &mut WindowContext,
-    ) -> Task<Result<SlashCommandOutput>> {
+    ) -> Task<SlashCommandResult> {
         let prompt_builder = self.prompt_builder.clone();
         cx.spawn(|_cx| async move {
             let text = prompt_builder.generate_workflow_prompt()?;