zed-editor: options to generate debug.json

Add `mutableUserDebug` and `userDebug` options to generate `debug.json` file.
The options are heavily inspired by `mutableUserTasks` and `userTasks` options implementation.

Closes #8091

tests/modules/programs/zed-editor/debug-empty.nix

@@ -0,0 +1,83 @@
+{
+  config,
+  lib,
+  pkgs,
+  ...
+}:
+
+{
+  programs.zed-editor = {
+    enable = true;
+    package = config.lib.test.mkStubPackage { };
+    userDebug = [
+      {
+        label = "PHP: Listen to Xdebug";
+        adapter = "Xdebug";
+        request = "launch";
+        port = 9003;
+      }
+      {
+        label = "PHP: Debug this test";
+        adapter = "Xdebug";
+        request = "launch";
+        program = "vendor/bin/phpunit";
+        args = [
+          "--filter"
+          "$ZED_SYMBOL"
+        ];
+      }
+    ];
+  };
+
+  home.homeDirectory = lib.mkForce "/@TMPDIR@/hm-user";
+
+  nmt.script =
+    let
+      preexistingDebug = builtins.toFile "preexisting.json" "";
+
+      expectedContent = builtins.toFile "expected.json" ''
+        [
+          {
+            "adapter": "Xdebug",
+            "args": [
+              "--filter",
+              "$ZED_SYMBOL"
+            ],
+            "label": "PHP: Debug this test",
+            "program": "vendor/bin/phpunit",
+            "request": "launch"
+          },
+          {
+            "adapter": "Xdebug",
+            "label": "PHP: Listen to Xdebug",
+            "port": 9003,
+            "request": "launch"
+          }
+        ]
+      '';
+
+      debugPath = ".config/zed/debug.json";
+      activationScript = pkgs.writeScript "activation" config.home.activation.zedDebugActivation.data;
+    in
+    ''
+      export HOME=$TMPDIR/hm-user
+
+      # Simulate preexisting debug
+      mkdir -p $HOME/.config/zed
+      cat ${preexistingDebug} > $HOME/${debugPath}
+
+      # Run the activation script
+      substitute ${activationScript} $TMPDIR/activate --subst-var TMPDIR
+      chmod +x $TMPDIR/activate
+      $TMPDIR/activate
+
+      # Validate the merged debug
+      assertFileExists "$HOME/${debugPath}"
+      assertFileContent "$HOME/${debugPath}" "${expectedContent}"
+
+      # Test idempotency
+      $TMPDIR/activate
+      assertFileExists "$HOME/${debugPath}"
+      assertFileContent "$HOME/${debugPath}" "${expectedContent}"
+    '';
+}