translation: lint fix + more migration

[davidtwco]

• Unfortunately, the diagnostic lints are very broken and trigger much more often than they should. This PR corrects the conditional which checks if the function call being made is to a diagnostic function so that it returns in every intended case.
• The rustc_lint_diagnostics attribute is used by the diagnostic translation/struct migration lints to identify calls where non-translatable diagnostics or diagnostics outwith impls are being created. Any function used in creating a diagnostic should be annotated with this attribute so this PR adds the attribute to many more functions.
• Port the diagnostics from the rustc_privacy crate and enable the lints for that crate.

r? @compiler-errors