klipper: Add an action to copy the QR image

Add the ability to copy the generated QR image, by toolbutton and the standard shortcut (Ctrl-C)

Reason for the change

This complements the ability to drag the QR image for direct use in a more discoverable way.

The motivation for this MR was direct feedback at the akademy-es convention. It wasn't clear to the users how to use the generated QR elsewhere (something that was thought useful) and that it can also be dragged and dropped (I discovered that when looking at the code)

Test plan

1. On any item of the clipboard history, click the button to generate a QR code

2. Copy the QR image

   2a. by clicking the button using the mouse

   2b. by activating the button using the keyboard (space)

   2c. pressing Ctrl-C

3. The QR image is added to the clipboard and can be pasted elsewhere

Screenshots or screen recordings

@teams/usability