Allow deconstruct guardrails

[sparr]

Summary

Content "Highway guard rails can be deconstructed"

Purpose of change

Guard rails can only be bashed, not otherwise deconstructed.

Describe the solution

Since they are usually held together with a few bolts or rivets, a prying tool should be able to get them apart with much less damage than bashing. So I added a deconstruct option.

Describe alternatives you've considered

Testing

I'll un-draft when I've tested thoroughly.

Additional context

I also changed the three highway/road guardrail definitions to copy-from a single abstract. They are identical other than the underlying terrain type.