Highlight whole row in picker menus

[ChrHorn]

This is for themes that use bg to highlight the selection in picker menus.
Makes it easier to navigate, looks cleaner, and is in line with the style of the autocomplete menu.

before:

after:

Not 100% sure if this is still needed:

helix/helix-term/src/ui/picker.rs

Lines 638 to 639 in fbb200b

	} else if is_active {
	selected.patch(span.style)

[sudormrfbin]

Thanks!