This adds the -verify-ignore-unrelated flag. When -verify is used without -verify-ignore-unrelated, diagnostics emitted in buffers other than the main file and those passed with -verify-additional-file (except diagnostics emitted at <unknown>:0) will now result in an error. They were previously ignored. The old behaviour is still available as opt-in using -verify-ignore-unrelated, but by being strict by default it should make it harder to accidentally miss diagnostics.
To avoid unnecessary performance overhead, -verify-additional-file is still required to parse the expected-* directives in files other than the main file.
These are tests that fail in the next commit without this flag. This
does not add -verify-ignore-unrelated to all tests with -verify, only
the ones that would fail without it. This is NFC since this flag is
currently a no-op.
Move the logic from `FailureDiagnostic::resolveType` into
`Solution::simplifyType` to allow completion to use it too. While
here, also handle cases where the placeholder is from a different
member of the equivalence class to the generic parameter.
`participatesInInference` is now always true for
a non-empty body, remove it along with the separate
type-checking logic such that empty bodies are
type-checked together with the context.
