compiler/ByteCode: Allow up to 2^32 local labels

This is a small refactoring and bug-fix for the bytecode interpreter, fixing #14334 (closed). In short we:

• Clean-up some stylistic issues I stumbled across
• Make LocalLabel a newtype
• Widen LocalLabel to Word32, fixing #14334 (closed)

To do the latter we use the existing long-jump support, extending the long-jump check to account for the fact that we may have more than 2^16 labels.