Add option to show operand stack's types in disassembly

[fitzgen]

When debugging some fiddly wasm bits I often annotate the WAT disassembly with the types on the stack in between each instruction:

;; []
i32.const 32
;; [i32]
i32.const 10
;; [i32 i32]
i32.add
;; [i32]

Would be nice if we added a flag to wasm-tools print to do this automatically.

I guess wasmprinter can handle invalid Wasm at the moment, so we would have to maybe make this best effort or require valid input for when this is enabled or something.

[alexcrichton]

The main tricky part here is that wasmprinter knows nothing of the type signatures of instructions, it "just" prints them and their opcode strings. Adding all the type information would be a pretty big change relative to what's done today

[fitzgen]

Oh I was imagining it would have a wasmparser::Validator when this option was enabled.

[alexcrichton]

Now that's a neat idea yeah! Could even do something like ;; [ ... ERROR ...] on validation failure