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.nix

@@ -0,0 +1,31 @@
+{
+  description = "High-performance, multiplayer code editor from the creators of Atom and Tree-sitter";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs?ref=nixos-unstable";
+  };
+
+  outputs =
+    { self, nixpkgs }:
+    let
+      inherit (self) outputs;
+      systems = [
+        "aarch64-linux"
+        "x86_64-linux"
+        "aarch64-darwin"
+        "x86_64-darwin"
+      ];
+      forAllSystems = nixpkgs.lib.genAttrs systems;
+    in
+    {
+      devShells = forAllSystems (
+        system:
+        let
+          pkgs = import nixpkgs { inherit system; };
+        in
+        {
+          default = import ./shell.nix { inherit pkgs; };
+        }
+      );
+    };
+}