Improve Zed prompts for file path selection (#32014)

Part of https://github.com/zed-industries/zed/discussions/31653
`"use_system_path_prompts": false` is needed in settings for these to
appear as modals for new file save and file open.

Fixed a very subpar experience of the "save new file" Zed modal,
compared to a similar "open file path" Zed modal by uniting their code.

Before:


https://github.com/user-attachments/assets/c4082b70-6cdc-4598-a416-d491011c8ac4


After:



https://github.com/user-attachments/assets/21ca672a-ae40-426c-b68f-9efee4f93c8c


Also 

* alters both prompts to start in the current worktree directory, with
the fallback to home directory.
* adjusts the code to handle Windows paths better

Release Notes:

- Improved Zed prompts for file path selection

---------

Co-authored-by: Smit Barmase <heysmitbarmase@gmail.com>

crates/file_finder/src/open_path_prompt_tests.rs

@@ -37,7 +37,7 @@ async fn test_open_path_prompt(cx: &mut TestAppContext) {
 
     let project = Project::test(app_state.fs.clone(), [path!("/root").as_ref()], cx).await;
 
-    let (picker, cx) = build_open_path_prompt(project, cx);
+    let (picker, cx) = build_open_path_prompt(project, false, cx);
 
     let query = path!("/root");
     insert_query(query, &picker, cx).await;
@@ -111,7 +111,7 @@ async fn test_open_path_prompt_completion(cx: &mut TestAppContext) {
 
     let project = Project::test(app_state.fs.clone(), [path!("/root").as_ref()], cx).await;
 
-    let (picker, cx) = build_open_path_prompt(project, cx);
+    let (picker, cx) = build_open_path_prompt(project, false, cx);
 
     // Confirm completion for the query "/root", since it's a directory, it should add a trailing slash.
     let query = path!("/root");
@@ -204,7 +204,7 @@ async fn test_open_path_prompt_on_windows(cx: &mut TestAppContext) {
 
     let project = Project::test(app_state.fs.clone(), [path!("/root").as_ref()], cx).await;
 
-    let (picker, cx) = build_open_path_prompt(project, cx);
+    let (picker, cx) = build_open_path_prompt(project, false, cx);
 
     // Support both forward and backward slashes.
     let query = "C:/root/";
@@ -251,6 +251,54 @@ async fn test_open_path_prompt_on_windows(cx: &mut TestAppContext) {
     );
 }
 
+#[gpui::test]
+async fn test_new_path_prompt(cx: &mut TestAppContext) {
+    let app_state = init_test(cx);
+    app_state
+        .fs
+        .as_fake()
+        .insert_tree(
+            path!("/root"),
+            json!({
+                "a1": "A1",
+                "a2": "A2",
+                "a3": "A3",
+                "dir1": {},
+                "dir2": {
+                    "c": "C",
+                    "d1": "D1",
+                    "d2": "D2",
+                    "d3": "D3",
+                    "dir3": {},
+                    "dir4": {}
+                }
+            }),
+        )
+        .await;
+
+    let project = Project::test(app_state.fs.clone(), [path!("/root").as_ref()], cx).await;
+
+    let (picker, cx) = build_open_path_prompt(project, true, cx);
+
+    insert_query(path!("/root"), &picker, cx).await;
+    assert_eq!(collect_match_candidates(&picker, cx), vec!["root"]);
+
+    insert_query(path!("/root/d"), &picker, cx).await;
+    assert_eq!(
+        collect_match_candidates(&picker, cx),
+        vec!["d", "dir1", "dir2"]
+    );
+
+    insert_query(path!("/root/dir1"), &picker, cx).await;
+    assert_eq!(collect_match_candidates(&picker, cx), vec!["dir1"]);
+
+    insert_query(path!("/root/dir12"), &picker, cx).await;
+    assert_eq!(collect_match_candidates(&picker, cx), vec!["dir12"]);
+
+    insert_query(path!("/root/dir1"), &picker, cx).await;
+    assert_eq!(collect_match_candidates(&picker, cx), vec!["dir1"]);
+}
+
 fn init_test(cx: &mut TestAppContext) -> Arc<AppState> {
     cx.update(|cx| {
         let state = AppState::test(cx);
@@ -266,11 +314,12 @@ fn init_test(cx: &mut TestAppContext) -> Arc<AppState> {
 
 fn build_open_path_prompt(
     project: Entity<Project>,
+    creating_path: bool,
     cx: &mut TestAppContext,
 ) -> (Entity<Picker<OpenPathDelegate>>, &mut VisualTestContext) {
     let (tx, _) = futures::channel::oneshot::channel();
     let lister = project::DirectoryLister::Project(project.clone());
-    let delegate = OpenPathDelegate::new(tx, lister.clone());
+    let delegate = OpenPathDelegate::new(tx, lister.clone(), creating_path);
 
     let (workspace, cx) = cx.add_window_view(|window, cx| Workspace::test_new(project, window, cx));
     (