Move Arbitrary instances from cardano-ledger

[neilmayhew]

Description

Move these instances closer to their types. This enables us to write better tests for cardano-base libraries.

Checklist

• Commit sequence broadly makes sense and commits have useful messages
• New tests are added if needed and existing tests are updated
• All visible changes are prepended to the latest section of a CHANGELOG.md for the affected packages.
  New section is never added with the code changes. (See RELEASING.md)
• When applicable, versions are updated in .cabal and CHANGELOG.md files according to the
  versioning process.
• The version bounds in .cabal files for all affected packages are updated.
  If you change the bounds in a cabal file, that package itself must have a version increase. (See RELEASING.md)
• Self-reviewed the diff

[lehins]

fromShort already performs the check for pinnedness: https://hackage-content.haskell.org/package/bytestring-0.11.5.4/docs/src/Data.ByteString.Short.Internal.html#fromShort

Suggested change

	byteArrayToByteString ba@(ByteArray ba#)
	| isByteArrayPinned ba =
	BS.fromForeignPtr (pinnedByteArrayToForeignPtr ba#) 0 (sizeofByteArray ba)
	| otherwise = SBS.fromShort (byteArrayToShortByteString ba)
	byteArrayToByteString ba = SBS.fromShort (byteArrayToShortByteString ba)

FTR. It didn't used to before in older versions of bytestring, hence the original implementation