JS/wasm CI

We should setup CI for the upcoming JS and wasm backends.

For the JS backend the following packages are needed from the CI environment (docker images):

emscripten version 3.14 or better
llvm 15
(@TerrorJack: does the wasm backend need something else?)

Build instructions for the JS backend can be found on https://gitlab.haskell.org/ghc/ghc/-/wikis/javascript-backend

Note that for now the testsuite doesn't fully pass. We expect it to pass before the merge (be it by disabling the most problematic tests when the JS backend is used).

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information