Wrapped it in a method so we can take advantage of TRY(). I chose not to
make failure here stop the Browser process, but just to cancel loading
any more search engines.
This opens the DOM Inspector window, with the target element already
selected. (If the window is already open, it just selects the element.)
Note that this only applies to single-process mode for now. In OOP mode,
the "inspect element" action is disabled.
It was very confusing for every Tab to have their own GUI::Menubar that
got dynamically swapped in/out when switching tabs.
This change moves us to a single menubar per window, and BrowserWindow
is the owner of its own menubar.
Having so much the logic and lambdas in main() was getting unwieldy.
Moving it into a class simplifies this, and also opens up a path
towards supporting "Open in New Window" :^)
