Modify high-contrast icon to be consistent with other built-in packs

The current icon for the 'high-contrast' built-in pack on Minecraft: Java edition is not consistent with other icons, creating an incoherent experience.

Instead of how the current icon is rendered (using a non-antialiased low-resolution isometric view of the high-contrast grass icon), it should instead be rendered in the same style and proportions as the other two icons to help promote visual consistency.