wasm-bindgen version of the Instruction struct.
This duplication is required until https://github.com/rustwasm/wasm-bindgen/issues/3671
is fixed. This must not diverge from the regular non-wasm Instruction struct.
Get the current stack height, transaction-level instructions are height
TRANSACTION_LEVEL_STACK_HEIGHT, fist invoked inner instruction is height
TRANSACTION_LEVEL_STACK_HEIGHT + 1, etc…