Add Nix/NixOS dev-shell (#13407)

This PR adds a Nix/NixOS development-shell (`shell.nix`), which is based
on the upstream
[nixpkgs](c5d4d45811/pkgs/by-name/ze/zed-editor/package.nix),
as well as its corresponding `flake.nix` file.

To use it, run either the `nix-shell` command (uses the `shell.nix`
file), or the newer but experimental `nix develop` command (uses
`flake.nix`)

~~This has not been tested on macOS, tho preliminary code is there to
try and support it, feel free to report any issues.~~ Zed unfortunately
doesn't build on nix-darwin (see
https://github.com/NixOS/nixpkgs/issues/320084), so this PR doesn't aim
to add darwin support.

---

Release Notes:

- N/A

---------

Signed-off-by: xtrm <oss@xtrm.me>
Co-authored-by: Niklas Korz <niklas@niklaskorz.de>

flake.lock

@@ -0,0 +1,27 @@
+{
+  "nodes": {
+    "nixpkgs": {
+      "locked": {
+        "lastModified": 1719690277,
+        "narHash": "sha256-0xSej1g7eP2kaUF+JQp8jdyNmpmCJKRpO12mKl/36Kc=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "2741b4b489b55df32afac57bc4bfd220e8bf617e",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "nixos-unstable",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
+    "root": {
+      "inputs": {
+        "nixpkgs": "nixpkgs"
+      }
+    }
+  },
+  "root": "root",
+  "version": 7
+}