Standing sign hitboxes are inaccurate

Created on request in the comments of MC-148581.

The bug

The hitbox for standing signs is quite inaccurate and barely represents the sign's shape at all. Despite the sign itself being composed of two cuboids, the hitbox of said sign only has one, and that one cuboid fits the sign's shape rather poorly.

How to reproduce

1. Place a sign on the ground

2. Target it

Expected results

The hitbox would match the sign's shape to a reasonable extent.

Actual results

The hitbox is a single cuboid that covers about half of the sign, missing out major portions and enclosing completely unrelated regions.

How to fix

As signs can be placed at angles which don't align perfectly with the axes, creating well-matching hitboxes for signs not facing in the compass directions may be a challenge. What should happen is:

• the post section should have a 2x2-pixel hitbox region to match its size and shape

• compass-direction facing signs can have a simple cuboid shape for their main sign region

• the other 12 signs may need multiple connected cuboids for a more fitting hitbox, similarly to what was done for the lectern