Remove `BorrowckErrors::tainted_by_errors`.

`BorrowckErrors` stores a mix of error and non-error diags in
`buffered`. As a result, it downgrades `DiagnosticBuilder`s to
`Diagnostic`s, losing the emission guarantees, and so has to use a
`tainted_by_errors` field to record whether an error has occurred.

This commit splits `buffered` into `buffered_errors` and
`buffered_non_errors`, keeping them as `DiagnosticBuilder`s and
preserving the emission guarantees.

This also requires fixing a bunch of incorrect lifetimes on
`DiagnosticBuilder` use points.

0 files changed, 0 insertions, 0 deletions