Port small fix

Author: jakebailey

internal/checker/grammarchecks.go

@@ -1921,7 +1921,7 @@ func (c *Checker) checkGrammarProperty(node *ast.Node /*Union[PropertyDeclaratio
 		if c.languageVersion < core.ScriptTargetES2015 && ast.IsPrivateIdentifier(propertyName) {
 			return c.grammarErrorOnNode(propertyName, diagnostics.Private_identifiers_are_only_available_when_targeting_ECMAScript_2015_and_higher)
 		}
-		if c.languageVersion < core.ScriptTargetES2015 && ast.IsAutoAccessorPropertyDeclaration(node) {
+		if c.languageVersion < core.ScriptTargetES2015 && ast.IsAutoAccessorPropertyDeclaration(node) && node.Flags&ast.NodeFlagsAmbient == 0 {
 			return c.grammarErrorOnNode(propertyName, diagnostics.Properties_with_the_accessor_modifier_are_only_available_when_targeting_ECMAScript_2015_and_higher)
 		}
 		if ast.IsAutoAccessorPropertyDeclaration(node) && c.checkGrammarForInvalidQuestionMark(node.AsPropertyDeclaration().PostfixToken, diagnostics.An_accessor_property_cannot_be_declared_optional) {

testdata/baselines/reference/submodule/compiler/accessorInAmbientContextES5.errors.txt

@@ -1,44 +1,26 @@
-accessorInAmbientContextES5.ts(4,14): error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
-accessorInAmbientContextES5.ts(5,21): error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
-accessorInAmbientContextES5.ts(6,22): error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
-accessorInAmbientContextES5.ts(7,29): error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
-accessorInAmbientContextES5.ts(12,18): error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
-accessorInAmbientContextES5.ts(19,18): error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
 accessorInAmbientContextES5.ts(25,14): error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
 
 
-==== accessorInAmbientContextES5.ts (7 errors) ====
+==== accessorInAmbientContextES5.ts (1 errors) ====
     // Should allow accessor in ambient contexts even when targeting ES5
 
     declare class AmbientClass {
         accessor prop1: string;
-                 ~~~~~
-!!! error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
         static accessor prop2: number;
-                        ~~~~~
-!!! error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
         private accessor prop3: boolean;
-                         ~~~~~
-!!! error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
         private static accessor prop4: symbol;
-                                ~~~~~
-!!! error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
     }
 
     declare namespace AmbientNamespace {
         class C {
             accessor prop: string;
-                     ~~~~
-!!! error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
         }
     }
 
     // Should also work in .d.ts files (simulated with declare)
     declare module "some-module" {
         export class ExportedClass {
             accessor value: any;
-                     ~~~~~
-!!! error TS18045: Properties with the 'accessor' modifier are only available when targeting ECMAScript 2015 and higher.
         }
     }