FIX - adopt new Diagnostic naming in newly migrated modules

FIX - ambiguous Diagnostic link in docs

UPDATE - rename diagnostic_items to IntoDiagnostic and AddToDiagnostic

[Gardening] FIX - formatting via `x fmt`

FIX - rebase conflicts. NOTE: Confirm wheather or not we want to handle TargetDataLayoutErrorsWrapper this way

DELETE - unneeded allow attributes in Handler method

FIX - broken test

FIX - Rebase conflict

UPDATE - rename residual _SessionDiagnostic and fix LintDiag link

compiler/rustc_span/src/symbol.rs

@@ -125,6 +125,7 @@ symbols! {
     Symbols {
         AcqRel,
         Acquire,
+        AddToDiagnostic,
         Alignment,
         Any,
         Arc,
@@ -176,7 +177,6 @@ symbols! {
         DecorateLint,
         Default,
         Deref,
-        Diagnostic,
         DiagnosticMessage,
         DirBuilder,
         Display,
@@ -210,6 +210,7 @@ symbols! {
         Implied,
         Input,
         Into,
+        IntoDiagnostic,
         IntoFuture,
         IntoIterator,
         IoRead,
@@ -282,7 +283,6 @@ symbols! {
         String,
         StructuralEq,
         StructuralPartialEq,
-        Subdiagnostic,
         SubdiagnosticMessage,
         Sync,
         T,