[WebAssembly] Add WebAssembly support to llvm-symbolizer

The only thing missing for basic llvm-symbolizer support is the ability on
lib/Object to get a wasm symbol's section ID, which allows sorting and
computation of the symbols' sizes.

Also, when the WasmAsmParser switches sections on new functions, also add the
section to the list of Dwarf sections if Dwarf is being generated for assembly;
this allows writing of simple tests.

Reviewers: sbc100, jhenderson, aardappel

Differential Revision: https://reviews.llvm.org/D73246