[llvm] [TableGen] Add `PreferSmallerInstructions` for Targets. (PR #83587)

[Simon Tatham via llvm-commits]

https://github.com/statham-arm approved this pull request.

I'm happy with this from the point of view of it filling in the missing comment I asked for on review #83436. I can't comment on whether the details of the specified preference order are _accurate_, though, so I have to rely on other reviewers for that :-)
 

https://github.com/llvm/llvm-project/pull/83587