Operations done before the main half float operation (like HAdd) were
managing a packed value instead of the unpacked one. Adding an unpacked
operation allows us to drop the per-operand MetaHalfArithmetic entry,
simplifying the code overall.
Some games call LDG at the top of a basic block, making the tracking
heuristic to fail. This commit lets the heuristic the decoded nodes as a
whole instead of per basic blocks.
This may lead to some false positives but allows it the heuristic to
track cases it previously couldn't.
