rewrite test to be closer to scalac production environment by using utest compileError

[tribbloid]

https://github.com/com-lihaoyi/utest#compile-error

Existing splain tests in scalac uses partest framework which invoke scalac directly (instead of scala reflect Toolbox). We should strive to do the same.

I have created a new acceptance submodule, we can gradually move our existing tests to be under it

[tribbloid]

blocked by com-lihaoyi/utest#258

Wondering if other libraries are doing similar thing

[tribbloid]

so far, no response, but I end up using scala nsc in runtime, the result seems to be quite similar to what partest is using. So I don't think it is a problem anymore.

Compile-time tests will be in the "acceptance" module. Will have to either wait for a fix or craft our own tool

[tribbloid]

end up crafting our own tool (TryCompile.Static), acceptance tests is working despite that it only covers a fraction of features, closed