auto find text fragment by xia_sava

1. Scroll to Text

When you transit to a URL with a fragment `#:~:text=foobar`, this add-on automatically searches for `foobar` in the page and scrolls to the first position of the matches.

2. Selection to Fragment

Selecting a string in the page and pressing the add-on button, this add-on creates a `#:~:text=foobar` fragment, and transitions to the URL, and copies the URL to the clipboard.