V8: Repeatable string hover + move handle styling

[kjac]

Prerequisites

• I have added steps to test this contribution in the description below

If there's an existing issue for this PR then this fixes: #4386

Description

As #4386 points out, the hover effect for the umb-multiple-textbox "Add" link isn't consistent with the "Add" link of the treenode pickers.

As it turns out, the umb-multiple-textbox "Add" link actually inherits its styles from umb-node-preview-add (used by the treenode pickers), but the hover effect hasn't been included. This PR fixes it.

I have also added a "move" cursor effect on the move handle for the text strings, as this is also in line with the styling elsewhere.

The whole thing looks something like this:

[emmaburstow]

Dearest @kjac,

I am writing this letter to thank you sincerely for the pull request you have herein submitted. You are truly a gentleman and a scholar and we are eternally grateful for your diligence, your assiduousness and your rigour. Long may it continue.

Yours sincerely,

Emma

[kjac]

So let it be written, so let it be done.

Sincerely,

Kenn.

[clausjensen]

Thanks for the pr @kjac :)