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>

crates/cli/Cargo.toml

@@ -34,6 +34,10 @@ util.workspace = true
 tempfile.workspace = true
 rayon.workspace = true
 
+[dev-dependencies]
+serde_json.workspace = true
+util = { workspace = true, features = ["test-support"] }
+
 [target.'cfg(any(target_os = "linux", target_os = "freebsd"))'.dependencies]
 exec.workspace = true
 fork.workspace = true