SI-7683 Enable -Ystop-before:typer

Allows a plugin to run before typer without incurring typechecking.

The test is that a plugin doesn't run when stopping after parser,
and that the truncated compilation run also succeeds, since
updating check files for the output of -Xshow-phases is tedious.
Merge pull request #4180 from som-snytt/issue/7683

SI-7683 Enable -Ystop-before:typer