IRBuilder is a utility for turning arbitrary valid streams of Wasm instructions into valid Binaryen IR. It is already used in the text parser, so now use it in the binary parser as well. Since the IRBuilder API for building each intruction requires only the information that the binary and text formats include as immediates to that instruction, the parser is now much simpler than before. In particular, it does not need to manage a stack of instructions to figure out what the children of each expression should be; IRBuilder handles this instead. There are some differences between the IR constructed by IRBuilder and the IR the binary parser constructed before this change. Most importantly, IRBuilder generates better multivalue code because it avoids eagerly breaking up multivalue results into individual components that might need to be immediately reassembled into a tuple. It also parses try-delegate more correctly, allowing the delegate to target arbitrary labels, not just other `try`s. There are also a couple superficial differences in the generated label and scratch local names. As part of this change, add support for recording binary source locations in IRBuilder.