feat(compiler): support safe keyed read expressions (#41911)

Currently we support safe property (`a?.b`) and method (`a?.b()`) accesses, but we don't handle safe keyed reads (`a?.[0]`) which is inconsistent. These changes expand the compiler in order to support safe key read expressions as well.

PR Close #41911

packages/compiler/test/expression_parser/utils/validator.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {AST, Binary, BindingPipe, Chain, Conditional, FunctionCall, ImplicitReceiver, Interpolation, KeyedRead, KeyedWrite, LiteralArray, LiteralMap, LiteralPrimitive, MethodCall, ParseSpan, PrefixNot, PropertyRead, PropertyWrite, Quote, RecursiveAstVisitor, SafeMethodCall, SafePropertyRead, Unary} from '../../../src/expression_parser/ast';
+import {AST, Binary, BindingPipe, Chain, Conditional, FunctionCall, ImplicitReceiver, Interpolation, KeyedRead, KeyedWrite, LiteralArray, LiteralMap, LiteralPrimitive, MethodCall, ParseSpan, PrefixNot, PropertyRead, PropertyWrite, Quote, RecursiveAstVisitor, SafeKeyedRead, SafeMethodCall, SafePropertyRead, Unary} from '../../../src/expression_parser/ast';
 
 import {unparse} from './unparser';
 
@@ -113,6 +113,10 @@ class ASTValidator extends RecursiveAstVisitor {
   visitSafePropertyRead(ast: SafePropertyRead, context: any): any {
     this.validate(ast, () => super.visitSafePropertyRead(ast, context));
   }
+
+  visitSafeKeyedRead(ast: SafeKeyedRead, context: any): any {
+    this.validate(ast, () => super.visitSafeKeyedRead(ast, context));
+  }
 }
 
 function inSpan(span: ParseSpan, parentSpan: ParseSpan|undefined): parentSpan is ParseSpan {