gap: Add runtime tests

[mkoeppe]

Adding tests as suggested in #5965 (comment)

FYI @wangyenshu @ChrisJefferson

[wangyenshu]

The documentation for gap wasm build is here https://github.com/gap-system/gap/tree/master/etc/emscripten. For a working website, the steps in https://github.com/gap-system/gap/blob/master/etc/emscripten/assemble-website.sh is needed.

[ChrisJefferson]

I don't know how much of a test you are happy to run. If a copy of GAP's test directory is available, Read("tst/testinstall.g");would be best, but it would take a while. If GASMAN is broken (as I suspect when ASYNCIFY was removed), these tests won't be enough to discover that as they aren't doing enough work to cause the GC to activate and garbage collection to not work correctly.

[mkoeppe]

A specific test that exercises the GC (GASMAN) would be most valuable.