Support no-capture behavior in wasm-bindgen-test

[Ekleog]

Note: this is still a draft, I need to put that behind a config option. But before I complete it all, I wanted to get an idea what y'all think about this?

My context is, I want to fuzz a crate of mine that needs to run in a browser. I cannot fuzz for now, because fuzzers don't support wasm32. So I want to at least have a very long-running proptest that generates random data.

But then in order to be able to know what's happening, I now need to have a view of what the test actually displays, so that I can distinguish between "running fine" and "deadlocked/panicked".

So before I turn it into a proper configuration option, WDYT about this change?