Add hoverable placeholder menu for custom paths

[a1156883061]

Add hoverable placeholder menu for convenient input placeholder when custom game save path

[mtkennerly]

Hi! Thanks for your PR. I like that this helps make the placeholders easier to discover.

The only change I'd like to request is that I don't like how the menu opens on hover. I'd rather have it require a click like the other three-dot buttons, and then just insert at the end of the text field. I understand the hover lets us insert by cursor position, but the way the menu closes if you scroll too much and the way insertion interacts with highlighted text don't feel so good to me.

[a1156883061]

Changed to click to open popupmenu, and still could insert by cursor

[mtkennerly]

Thanks :D