[Blazor] Way to run the E2E tests against the multithreaded runtime

[javiercn]

We should have a way to run the E2E tests against the multithreaded wasm runtime that is easy and convenient (like specifying an environment variable/build)

[SteveSandersonMS]

Starting point: https://gist.github.com/SteveSandersonMS/b852b53515dab22c584ec2ffd13bf397