paths: Replace lazy_static! with OnceLock (#13213)

This PR replaces the `lazy_static!` usages in the `paths` crate with
`OnceLock` from the standard library.

This allows us to drop the `lazy_static` dependency from this crate.

The paths are now exposed as accessor functions that reference a private
static value.

Release Notes:

- N/A

crates/assistant/src/prompt_library.rs

@@ -20,7 +20,6 @@ use gpui::{
 use heed::{types::SerdeBincode, Database, RoTxn};
 use language::{language_settings::SoftWrap, Buffer, LanguageRegistry};
 use parking_lot::RwLock;
-use paths::PROMPTS_DIR;
 use picker::{Picker, PickerDelegate};
 use rope::Rope;
 use serde::{Deserialize, Serialize};
@@ -49,7 +48,7 @@ actions!(
 /// Init starts loading the PromptStore in the background and assigns
 /// a shared future to a global.
 pub fn init(cx: &mut AppContext) {
-    let db_path = PROMPTS_DIR.join("prompts-library-db.0.mdb");
+    let db_path = paths::prompts_dir().join("prompts-library-db.0.mdb");
     let prompt_store_future = PromptStore::new(db_path, cx.background_executor().clone())
         .then(|result| future::ready(result.map(Arc::new).map_err(Arc::new)))
         .boxed()