Add generic window icons (#1045)

* Add generic `app-window` icon

* Update icons/app-window.svg

Co-authored-by: Karsa <contact@karsa.org>

* Update icons/app-window.json

---------

Co-authored-by: Karsa <contact@karsa.org>

icons/app-window.json

@@ -0,0 +1,12 @@
+{
+  "$schema": "../icon.schema.json",
+  "tags": [
+    "application",
+    "executable"
+  ],
+  "categories": [
+    "design",
+    "files",
+    "layout"
+  ]
+}

icons/app-window.svg

@@ -0,0 +1,16 @@
+<svg
+  xmlns="http://www.w3.org/2000/svg"
+  width="24"
+  height="24"
+  viewBox="0 0 24 24"
+  fill="none"
+  stroke="currentColor"
+  stroke-width="2"
+  stroke-linecap="round"
+  stroke-linejoin="round"
+>
+  <rect x="2" y="4" width="20" height="16" rx="2" />
+  <path d="M10 4v4" />
+  <path d="M2 8h20" />
+  <path d="M6 4v4" />
+</svg>