The Rust bytecode dumper now formats exception handler labels, raw
operands, builtins, labels, and registers. Remove the C++ dump-only
formatters and flatten Operand to expose only the runtime value-array
layout that C++ still observes.
The Rust bytecode generator now owns basic block construction.
The old C++ BasicBlock class no longer has any users.
Label no longer needs to translate from BasicBlock.
Remove the now-empty Label.cpp from the build as well.
This reverts commit c14173f651. We
should only annotate the minimum number of symbols that external
consumers actually use, so I am starting from scratch to do that
