Replace Quick Fix label in hover popup with lightbulb icon

[jwortmann]

Currently there is a "Quick Fix" prefix for when code actions are shown in the hover popup.

This is a suggestion to replace that label with the lightbulb icon, because

• it saves a little bit of space and subjectively looks nicer
• we filter out non-quickfix actions for the popups, but some servers omit the code action kind and then there might still be actions included which are no quickfixes. I think the lightbulb symbol is more generic and fits better in that case

I used the orange color from Mariana, but I think it should look okay in both dark and light color schemes.