indicate bitfield properties in class reference

**Your Godot version:** 4.4.1

**Issue description:**
In the class reference put `bitfield` to indicate that a property its meant to be used as such.

ie: `CollisionBody3D.collision_mask [default: 1] bitfield`

Start with the class reference entry for CollisionBody3D.collision_mask and check how property metadata is rendered. Done means the reference visibly labels bitfield properties, including this property, without changing unrelated reference output.

Written by the indexing model from the issue text.