WebAssembly: see if "-d symbols" can be improved

Issue https://github.com/google/bloaty/issues/184 indicates that `-d symbols` is sometimes returning not very useful information like:

```
FILE SIZE VM SIZE
-------------- --------------
63.8% 313Ki NAN% 0 [538 Others]
4.1% 20.3Ki NAN% 0 func[482]
3.5% 17.3Ki NAN% 0 [section Data]
3.2% 15.9Ki NAN% 0 func[514]
3.0% 14.9Ki NAN% 0 func[503]
2.3% 11.5Ki NAN% 0 func[528]
2.3% 11.0Ki NAN% 0 func[47]
1.6% 7.91Ki NAN% 0 func[513]
1.6% 7.67Ki NAN% 0 func[494]
1.6% 7.65Ki NAN% 0 func[505]
1.5% 7.59Ki NAN% 0 func[324]
1.4% 6.70Ki NAN% 0 func[323]
1.3% 6.16Ki NAN% 0 func[509]
1.2% 5.90Ki NAN% 0 func[523]
1.2% 5.84Ki NAN% 0 func[499]
1.2% 5.67Ki NAN% 0 func[418]
1.1% 5.61Ki NAN% 0 func[524]
1.1% 5.41Ki NAN% 0 func[478]
1.1% 5.36Ki NAN% 0 func[526]
0.9% 4.57Ki NAN% 0 func[507]
0.9% 4.56Ki NAN% 0 func[403]
100.0% 490Ki 100.0% 0 TOTAL
```

We want to get real function names here, instead `func[47]`. We should investigate whether these function names are available somewhere in the binary, whether in a symbol table or in DWARF debug info.