Enforce that raw lifetime identifiers must be valid raw identifiers

compiler/rustc_parse/src/errors.rs

@@ -2018,6 +2018,14 @@ pub(crate) struct CannotBeRawIdent {
     pub ident: Symbol,
 }
 
+#[derive(Diagnostic)]
+#[diag(parse_cannot_be_raw_lifetime)]
+pub(crate) struct CannotBeRawLifetime {
+    #[primary_span]
+    pub span: Span,
+    pub ident: Symbol,
+}
+
 #[derive(Diagnostic)]
 #[diag(parse_keyword_lifetime)]
 pub(crate) struct KeywordLifetime {