add WASM testing to CI

[BurntSushi]

Someone on reddit mentioned that they are hoping WASM support continues to work through the release migration.

The regex crate has never promised WASM support and it is not being tested in CI. With that said, there are plenty of folks using the regex crate in a WASM context, notably regex101.com, so breaking that is not really an option. But given that we aren't doing any testing with WASM, that seems like a problem.

I personally don't have a ton of experience with WASM (yet), so I would love if someone with more expertise in that domain could contribute a patch that adds testing to CI. If there are many different ways of testing CI, then we should have a discussion first. I would definitely like to minimize dependencies on external tooling as much as possible, unless they are mature and not likely to break.