Co-authored-by: Jamie Thompson <[email protected]>
Co-authored-by: Li Haoyi <[email protected]>

…test

Traits are forbidden in source code from having secondary constructors,
which is what the current transform would generate.

Trait parameters are encoded in concrete implementing classes as getter methods,
perhaps unroll could provide default implementations, but this is unexplored.

Now, all forwarders directly call the unrolled method.
This means that there is no need to resolve an invisible method,
so the "hack" using TERMREFdirect is no longer needed.

This increases bytecode size but reduces stack depth.

Also removed scala.annotation.internal.UnrolledForwarder,
as it is only needed for the TASTy hack.

Also standardise error messages as Declaration Errors

…yper

At typer, when transparent inline methods are expanded, unroll forwarders
are not yet generated.

So if we define forwarders for the first time, in the same compilation
unit that inlines a call to the forwarder, then it will fail.

Perhaps we can detect this and suspend the unit, otherwise it would seem
unreasonable complexity to generate forwarders in typer.