Browser: Popup menu in stylesheet inspector doesn't work

[nico]

We'll probably need something like 549f5fe for Userland/Applications/Browser too. Tab.{h,cpp} currently has RefPtr<GUI::Menu> m_select_dropdown and that has to move to the view impl.

However, as far as I can tell, that's currently LibWebView/OutOfProcessWebView, and that probably shouldn't have access to LibGUI (?).

[nico]

OutOfProcessWebView already depends on LibGUI, so short term putting it there looks like the clear path forward.