Use IRBuilder in the binary parser

[tlively]

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 trys. There are also a couple superficial differences in the generated label and scratch local names.

There are two remaining bugs: First, support for creating DWARF location spans is missing because IRBuilder does not have an API for that yet (but source map locations work fine). Second, IRBuilder generates pops inside nameless blocks in some circumstances involving stacky code. This is currently an IR validation error, so #6950 will have to be resolved before this can land.

This change also makes the binary parser significantly slower (by about 50%). The lowest hanging performance fruit seems to be tracking branch targets in IRBuilder to avoid having to scan for branches when finalizing blocks.