lint: add diagnostic translation migration lints

Introduce allow-by-default lints for checking whether diagnostics are
written in `SessionDiagnostic`/`AddSubdiagnostic` impls and whether
diagnostics are translatable. These lints can be denied for modules once
they are fully migrated to impls and translation.

Signed-off-by: David Wood <david.wood@huawei.com>

compiler/rustc_span/src/symbol.rs

@@ -125,6 +125,7 @@ symbols! {
     Symbols {
         AcqRel,
         Acquire,
+        AddSubdiagnostic,
         Alignment,
         Any,
         Arc,
@@ -169,6 +170,7 @@ symbols! {
         Decoder,
         Default,
         Deref,
+        DiagnosticMessage,
         DirBuilder,
         Display,
         DoubleEndedIterator,
@@ -253,11 +255,13 @@ symbols! {
         RustcEncodable,
         Send,
         SeqCst,
+        SessionDiagnostic,
         SliceIndex,
         Some,
         String,
         StructuralEq,
         StructuralPartialEq,
+        SubdiagnosticMessage,
         Sync,
         Target,
         ToOwned,
@@ -1205,6 +1209,7 @@ symbols! {
         rustc_layout_scalar_valid_range_end,
         rustc_layout_scalar_valid_range_start,
         rustc_legacy_const_generics,
+        rustc_lint_diagnostics,
         rustc_lint_query_instability,
         rustc_macro_transparency,
         rustc_main,