HackStudio: Add FindWidget

The find widget appears on Ctrl+F.

It uses the GUI::TextEditor search API to search for text, which also
takes care of highlighting the search results.

Userland/DevTools/HackStudio/FindWidget.gml

@@ -0,0 +1,32 @@
+@GUI::Widget {
+    name: "find_widget"
+    fill_with_background_color: true
+    shrink_to_fit: true
+    visible: false
+    layout: @GUI::HorizontalBoxLayout {
+        margins: [0, 0]
+    }
+
+    @GUI::TextBox {
+        name: "input_field"
+        max_width: 250
+    }
+
+    @GUI::Label {
+        name: "index_label"
+        max_width: 30
+        text: ""
+    }
+
+    @GUI::Button {
+        name: "next"
+        icon: "/res/icons/16x16/go-down.png"
+        max_width: 15
+    }
+
+    @GUI::Button {
+        name: "previous"
+        icon: "/res/icons/16x16/go-up.png"
+        max_width: 15
+    }
+}