Treat this as a constant reference for purpose of narrowing using aliased expressions (#54347)

src/compiler/checker.ts

@@ -26457,6 +26457,8 @@ export function createTypeChecker(host: TypeCheckerHost): TypeChecker {
 
     function isConstantReference(node: Node): boolean {
         switch (node.kind) {
+            case SyntaxKind.ThisKeyword:
+                return true;
             case SyntaxKind.Identifier:
                 if (!isThisInTypeQuery(node)) {
                     const symbol = getResolvedSymbol(node as Identifier);