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?

[daxpedda]

I'm not entirely sure what exactly you are trying to show in the shell, but in general it would be good if we align more with cargo test:

• We should show test results in the shell as soon as possible, no reason to wait until everything is done.
• Using --nocapture should I guess show the console output in the shell if there is any.

Currently the output in the shell is a complete mess, so any improvements on that front are appreciated.