Added Expect lint level and attribute (RFC-2383)

* Also added the `LintExpectationId` which will be used in future commits

compiler/rustc_errors/src/annotate_snippet_emitter_writer.rs

@@ -75,6 +75,7 @@ fn annotation_type_for_level(level: Level) -> AnnotationType {
         // FIXME(#59346): Not sure how to map this level
         Level::FailureNote => AnnotationType::Error,
         Level::Allow => panic!("Should not call with Allow"),
+        Level::Expect(_) => panic!("Should not call with Expect"),
     }
 }