wasm: set focus on canvas on new screen

This allows user to utilize the application without having to click on
it first to cause the focus-in event.

Change-Id: Ibc9582254dda91eb14ebcdf4b8ea4a4f862aa88d
Reviewed-by: Morten Johan Sørvig <morten.sorvig@qt.io>

src/plugins/platforms/wasm/qwasmscreen.cpp

@@ -54,6 +54,8 @@ QWasmScreen::QWasmScreen(const QString &canvasId)
     m_compositor = new QWasmCompositor(this);
     m_eventTranslator = new QWasmEventTranslator(this);
     updateQScreenAndCanvasRenderSize();
+    emscripten::val canvas = emscripten::val::global(m_canvasId.toUtf8().constData());
+    canvas.call<void>("focus");
 }
 
 QWasmScreen::~QWasmScreen()