Move Nix files into a nix directory

Move everything from `config` to the root level.

nvim/plugin/edit_alternate.lua

@@ -0,0 +1,40 @@
+vim.fn["edit_alternate#rule#add"]("php", function(filename)
+  if filename:find "Test.php$" then
+    filename = filename:gsub("Test.php$", ".php")
+
+    if filename:find "tests/src/" then
+      -- Drupal tests. Remove the `src/{type}` from the path.
+      return filename:gsub("tests/src/(.-)/", "src/")
+    else
+      return filename:gsub("tests/", "src/")
+    end
+  else
+    filename = filename:gsub(".php$", "Test.php")
+
+    if filename:find "modules/custom" then
+      -- Drupal test types.
+      local test_types = { "Functional", "FunctionalJavaScript", "Kernel", "Unit" }
+
+      for _, test_type in ipairs(test_types) do
+        local filename_with_test_type = filename:gsub("src/", string.format("tests/src/%s/", test_type))
+
+        -- Return the first matching test file that exists.
+        if vim.fn.filereadable(filename_with_test_type) == 1 then
+          return filename_with_test_type
+        end
+      end
+    end
+  end
+end)
+
+if vim.fn.filereadable "fractal.config.js" == 1 then
+  vim.fn["edit_alternate#rule#add"]("twig", function(filename)
+    return (filename:gsub("%.twig$", ".config.yml"))
+  end)
+
+  vim.fn["edit_alternate#rule#add"]("yml", function(filename)
+    return (filename:gsub("%.config.yml$", ".twig"))
+  end)
+end
+
+vim.keymap.set("n", "<leader>ea", "<CMD>EditAlternate<CR>", { silent = true })