BrowserSim launch via toolbar/command should guess which url based on current selection/editor

Right now when you launch browsersim it simply opens on a blank page.

It should look at the current editor/selection to see if it has something that should be opened.

i.e. when having a browser editor open on some url we should take that url and open - that would allow you to use Run As ... as "normal" and from there start mobile browser if wanted to.

similar if having a file selected we should open that file.