Add Environment::runWithStringResults to enable better Lua console REPL

[GinjaNinja32]

There may be a better design here - happy to adjust if you have suggestions.

[daid]

Not a fan of so much extra code which is mostly duplicated with minor variations. I think the only thing you currently cannot do yet is the MULTIRET, the rest is sort of doable outside of SP changes.

[GinjaNinja32]

hmm. Might be able to merge the two paths into one with something like

Result<void> runStrings(code, name, callback) {
    return runImpl(code, name, [](firstResult) {
        // string code
    });
}
Result<T> runResult(code, name) {
    return runImpl(code, name, [](firstResult) {
        if (lua_gettop(L) < firstResult) {
            // no returned value, convert as if nil
        } else {
            // convert index `firstResult` as normal
        }
        // pop?
    });
}
Result<T> runImpl(code, name, std::function<Result<T>(int firstResult)> handleResults) {
    // MULTRET code through L86
    return handleResults(top - 1);
}

[daid]

daid/EmptyEpsilon@183db32
5ff9371
This is my attempt in the ECS branch.

[GinjaNinja32]

that implementation looks good and does what I wanted from this 👍