add copy highlight text botton on menu

[seyeeL]

I wish there was an option to copy this highlight on the popup when I click on an existing highlight, instead of having to copy it again with the mouse

[robertknight]

I'm not sure that we want to add extra buttons to this UI, but we could add a keyboard shortcut that either copies the highlighted text or sets the browser selection to the highlighted text, from there you can right click or tap and click "Copy".