Report compiler version mismatches more visibly

Sometimes while working on nightly, there's old compilation artifacts for cargo check that get found by cargo check, and it fails with some errors that they were made with a different compiler version. If this happens to r-a, they are not very visible, at least in editors that don't show the errors list prominently, leading users to wonder why there's no diagnostics they expect to be there in the current file.

I'd like if this particular error were injected into the top of the file like unlinked module errors are currently, as it would cause my ide to show there being errors. Either that or maybe do a pop up like project model cargo checks do.

Start with the troubleshooting guide and compare how unlinked module errors are surfaced with how project-model cargo checks report failures. Investigate the compiler-version mismatch from cargo check and determine where its diagnostic can be made visible in the editor. Done means users reliably see an error indicator or popup when this mismatch prevents expected diagnostics.