Dedupe PromptBuilder construction (#23496)

This PR dedupes the construction of the `PromptBuilder`.

Previously this was constructed by both `assistant` and `assistant2`,
but now we construct it outside and pass it in.

Release Notes:

- N/A

crates/prompt_library/src/prompts.rs

@@ -2,7 +2,7 @@ use anyhow::Result;
 use assets::Assets;
 use fs::Fs;
 use futures::StreamExt;
-use gpui::AssetSource;
+use gpui::{AppContext, AssetSource};
 use handlebars::{Handlebars, RenderError};
 use language::{BufferSnapshot, LanguageName, Point};
 use parking_lot::Mutex;
@@ -56,6 +56,19 @@ pub struct PromptBuilder {
 }
 
 impl PromptBuilder {
+    pub fn load(fs: Arc<dyn Fs>, stdout_is_a_pty: bool, cx: &mut AppContext) -> Arc<Self> {
+        Self::new(Some(PromptLoadingParams {
+            fs: fs.clone(),
+            repo_path: stdout_is_a_pty
+                .then(|| std::env::current_dir().log_err())
+                .flatten(),
+            cx,
+        }))
+        .log_err()
+        .map(Arc::new)
+        .unwrap_or_else(|| Arc::new(Self::new(None).unwrap()))
+    }
+
     pub fn new(loading_params: Option<PromptLoadingParams>) -> Result<Self> {
         let mut handlebars = Handlebars::new();
         Self::register_built_in_templates(&mut handlebars)?;