Replace environment variable parser with zed --printenv outputting JSON (#32637)

Closes: https://github.com/zed-industries/zed/issues/32445
Follow-up to: https://github.com/zed-industries/zed/pull/31799

Release Notes:

- Improved handling of environment variables

---------

Co-authored-by: Conrad Irwin <conrad@zed.dev>

Cargo.lock

@@ -491,7 +491,6 @@ dependencies = [
  "anyhow",
  "futures 0.3.31",
  "gpui",
- "shlex",
  "smol",
  "tempfile",
  "util",
@@ -17355,6 +17354,7 @@ dependencies = [
  "serde",
  "serde_json",
  "serde_json_lenient",
+ "shlex",
  "smol",
  "take-until",
  "tempfile",