Fix ssh project history (#19683)

Use `Fs` instead of `std::fs` and do entry existence checks better:
* first, check the worktree entry existence without any FS checks
* then, only for local cases, use `Fs` to check for abs_path existence
of items, in case those came from single-filed worktrees that got closed
and removed.

Remote entries do not get file existence checks, so might try opening
previously removed buffers for now.

Release Notes:

- N/A

crates/project/src/project.rs

@@ -1875,11 +1875,7 @@ impl Project {
         })
     }
 
-    pub fn get_open_buffer(
-        &mut self,
-        path: &ProjectPath,
-        cx: &mut ModelContext<Self>,
-    ) -> Option<Model<Buffer>> {
+    pub fn get_open_buffer(&self, path: &ProjectPath, cx: &AppContext) -> Option<Model<Buffer>> {
         self.buffer_store.read(cx).get_by_path(path, cx)
     }
 
@@ -3295,17 +3291,10 @@ impl Project {
     }
 
     pub fn absolute_path(&self, project_path: &ProjectPath, cx: &AppContext) -> Option<PathBuf> {
-        let workspace_root = self
-            .worktree_for_id(project_path.worktree_id, cx)?
+        self.worktree_for_id(project_path.worktree_id, cx)?
             .read(cx)
-            .abs_path();
-        let project_path = project_path.path.as_ref();
-
-        Some(if project_path == Path::new("") {
-            workspace_root.to_path_buf()
-        } else {
-            workspace_root.join(project_path)
-        })
+            .absolutize(&project_path.path)
+            .ok()
     }
 
     /// Attempts to find a `ProjectPath` corresponding to the given path. If the path