[WebAssembly] Convert to new "dylink.0" section format

This format is based on sub-sections (like the "linking" and "name"
sections) and is therefore easier to extend going forward.

spec change: https://github.com/WebAssembly/tool-conventions/pull/170
binaryen change: https://github.com/WebAssembly/binaryen/pull/4141
wabt change:  https://github.com/WebAssembly/wabt/pull/1707
emscripten change: https://github.com/emscripten-core/emscripten/pull/15019

Differential Revision: https://reviews.llvm.org/D109595