cli: Allow opening non-existent paths (#43250)

Changes are made to `parse_path_with_position`:
we try to get the canonical, existing parts of
a path, then append the non-existing parts.

Closes #4441

Release Notes:

- Added the possibility to open a non-existing path using `zed` CLI
  ```
  zed path/to/non/existing/file.txt
  ```

Co-authored-by: Syed Sadiq Ali <sadiqonemail@gmail.com>

Cargo.lock

@@ -3086,6 +3086,7 @@ dependencies = [
  "rayon",
  "release_channel",
  "serde",
+ "serde_json",
  "tempfile",
  "util",
  "windows 0.61.3",