wast: Ordering of instructions is a bit disordered

[eqrion]

wast::Instruction [1] lists all instructions that can be parsed by WebAssembly. Currently it is neither sorted by name, encoding, or proposal. This makes it a bit hard to find where an instruction is, and I'd be happy to open a PR to sort it in some way.

@alexcrichton What do you think about sorting by proposal and then sorting by encoding within proposal?

[1]

wasm-tools/crates/wast/src/ast/expr.rs

Line 341 in e3f6090

Block(BlockType<'a>) : [0x02] : "block",

[alexcrichton]

Sounds reasonable to me!