new path picker (#11015)

Still TODO:

* Disable the new save-as for local projects
* Wire up sending the new path to the remote server

Release Notes:

- Added the ability to "Save-as" in remote projects

---------

Co-authored-by: Nathan <nathan@zed.dev>
Co-authored-by: Bennet <bennetbo@gmx.de>

crates/rpc/proto/zed.proto

@@ -769,6 +769,12 @@ message SaveBuffer {
     uint64 project_id = 1;
     uint64 buffer_id = 2;
     repeated VectorClockEntry version = 3;
+    optional ProjectPath new_path = 4;
+}
+
+message ProjectPath {
+    uint64 worktree_id = 1;
+    string path = 2;
 }
 
 message BufferSaved {