Umbrella task for items that need investigation/fix before WebAssembly merge

There are a few hacks and workarounds in Qt for WebAssembly that either work around bugs in Emscripten and the compiler tool chain, or they are hacks to fix issues we don't fully understand.

This task is meant as an umbrella task to collect all of them, so that we can make sure they are checked and updated later, before we make the port fully supported.