Redesign Worktree save API and make test_rescan_simple pass

This commit does too much. The first goal was to change our approach to saving new buffers so that we don't need to construct a File for an entry that doesn't exist. Rather than doing that, we call `Worktree::save_buffer_as` with the buffer handle, the path, and the contents. This then saves the buffer and returns a handle to a `File` that references an entry that actually exists. I needed to do this so that we can store an entry id on `File`.

In the process, I noticed intermittent test failures on `test_rescan_simple`, so I made some changes required to fix those related to our reuse of existing ids. Our previous approach of removing a path when inserting a new entry was broken, because of the recursive nature of `remove_path`. Instead, I simply recycle the id of an existing worktree entry with the same path if one is present, then allow it to be replaced.

zed/src/editor.rs

@@ -7,7 +7,7 @@ use crate::{
     settings::{Settings, StyleId},
     util::{post_inc, Bias},
     workspace,
-    worktree::File,
+    worktree::{File, Worktree},
 };
 use anyhow::Result;
 pub use buffer::*;
@@ -2506,8 +2506,18 @@ impl workspace::ItemView for Editor {
         Some(clone)
     }
 
-    fn save(&mut self, new_file: Option<File>, cx: &mut ViewContext<Self>) -> Task<Result<()>> {
-        self.buffer.update(cx, |b, cx| b.save(new_file, cx))
+    fn save(&mut self, cx: &mut ViewContext<Self>) -> Result<Task<Result<()>>> {
+        self.buffer.update(cx, |b, cx| b.save(cx))
+    }
+
+    fn save_as(
+        &mut self,
+        worktree: &ModelHandle<Worktree>,
+        path: &Path,
+        cx: &mut ViewContext<Self>,
+    ) -> Task<Result<()>> {
+        self.buffer
+            .update(cx, |b, cx| b.save_as(worktree, path, cx))
     }
 
     fn is_dirty(&self, cx: &AppContext) -> bool {