Helpbrowser: redirect http links to system browser (#7421)

* redirectToSystemBrowser class method

add said class method, used in *goTo (for IDE Helpbrowser) and
webView.onLinkActivated in HelpBrowser.init

Clicking on web links now opens a menu that gives user the option to open the link in either system default web browser or the web-unsafe built-in help browser.
I made sure this works both in the SCIDE helpbrowser and the one created through HelpBrowser.new().


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Co-authored-by: PyoungRyang Ko <pyoungryang.ko@googlemail.com>