Improve Ord docs

[Voultapher]

• Makes wording more clear and re-structures some sections that can be overwhelming for someone not already in the know.
• Adds examples of how not to implement Ord, inspired by various anti-patterns found in real world code.

Many of the wording changes are inspired directly by my personal experience of being confused by the Ord docs and seeing other people get it wrong as well, especially lately having looked at a number of Ord implementations as part of #128899.

Created with help by @orlp.

r​? @workingjubilee