This patch changes the LibJS bytecode to be a stream of instructions
packed one-after-the-other in contiguous memory, instead of a vector
of OwnPtr<Instruction>. This should be a lot more cache-friendly. :^)
Instructions are also devirtualized and instead have a type field
using a new Instruction::Type enum.
To iterate over a bytecode stream, one must now use
Bytecode::InstructionStreamIterator.
e7d69c5d3c