fix: Leap highlight are out of date

[GCBallesteros]

Support for leap is broken. At some leap must have changed it's highlight group names breaking the integration. They are currently:

• LeapMatch
• LeapLabel
• LeapBackdrop

This PR does two things:

1. Update the highlight group names
2. Modify the used colors to increase the usability of leap and bringing it more to line

The images below show screenshots for zenbones dark & light when Leap is active

Rationale for color change

Previously the labels used the same colors as IncSearch (bold white foreground over magenta background):
.

In my opinion this is not high contrast enough for how leap (or any other jump plugin) is used. In this kind of plugins labels are visible in practice for around 200 or 300 ms at most so you really need them to stand out. On the static picture the colors might look too strong but since they are only on the screen for a fraction of a second at a time they don't destroy the zenbones experience.

The new colors respect the previous hues but change the saturation and lightness. It also makes use of the LeapBackdrop group to further enhance readability.

[mcchrish]

Makes sense to me! Thanks a lot.

[GCBallesteros]

Thanks to you for the great themes!