Put JavaScript commands for WebActions in QStringLiteral

QWebEnginePage::runJavaScript and QQuickWebEngineView::runJavaScript
have QString parameters. Passing raw strings causes them to be passed
to the deprecated QString constructor, which causes warnings in the
compilation.

Change-Id: I072149ca85c94b2b94c7b5d9aa198eddd47460e8
Reviewed-by: Jüri Valdmann <juri.valdmann@qt.io>
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>