Demonstrate regression in #4949 for positions of quote-inlined code

[Blaisorblade]

Testcase moved here from #5009. Edited comment from there:

It seems to have been broken by #4949 (not by #4990, I rechecked). /cc @nicolasstucki

Reason: After #4949, calling from Test.main transparent function from the same file Test.assert2 causes no repositioning; but the output trees actually come from Macros so they must be repositioned. This was an existing bug (which affected sourcePos even earlier); to fix this without changing enclosedInlineds, one needs
a node Inlined(Macros.assertImpl(...), ...) around the quote body, in addition.

Especially if there can be both code from the transparent function and from the splice, we'd need something like

Inlined(assert2(...), ...,
  Inlined(Macros.assertImpl(...), ..., {
    printStack("assertImpl")
    println(Inlined(EmptyTree, Nil, Inlined(EmptyTree, Nil, x != 0)))
  })
)

We do need two EmptyTree around x != 0 to signal it does come from the original call site. Not 100% sure what goes in the ellipses.

PostTyper can strip the call as usual, no problem.

[Blaisorblade]

Readers will like a reference to code in PostTyper.transform producing this format, since they’ll need to keep them in sync.

[nicolasstucki]

Waiting for refactorings of #5132