Misc: Use automatic window positioning in more applications

This is a follow up to #2936 / d3e3b4ae56aa79d9bde12ca1f143dcf116f89a4c.

Affected programs:
- Applications: Browser (Download, View source, Inspect DOM tree, JS
  console), Terminal (Settings)
- Demos: Cube, Eyes, Fire, HelloWorld, LibGfxDemo, WebView,
  WidgetGallery
- DevTools: HackStudio, Inspector, Profiler
- Games: 2048, Minesweeper, Snake, Solitaire
- Userland: test-web

A few have been left out where manual positioning is done on purpose,
e.g. ClipboardManager (to be close to the menu bar) or VisualBuilder (to
preserve alignment of the multiple application windows).

Demos/WebView/main.cpp

@@ -42,7 +42,7 @@ int main(int argc, char** argv)
     auto& view = main_widget.add<WebContentView>();
     auto& statusbar = main_widget.add<GUI::StatusBar>();
     window->set_title("WebView");
-    window->set_rect(100, 100, 640, 480);
+    window->resize(640, 480);
     window->show();
 
     view.on_title_change = [&](auto& title) {