Added support for meta icon titles in input list options

[kevinansfield]

ref https://linear.app/tryghost/issue/MOM-80

• added support for metaIconTitle properties on list options to add title attributes to span that wraps the icon
  • span added because title attributes directly on the SVG do not show when hovering the mouse over
• updated demo app default search link content to match Ghost's meta data usage
• updated assertHTML e2e test util to allow a specific selector to be used
  • useful when wanting to asserting smaller parts of the editor content
  • allows for asserting Portal'ed content that appears outside the main editor element