add missing Error.isError feature flag

See https://github.com/tc39/test262/pull/4266#issuecomment-2419000590

features.txt

@@ -80,6 +80,10 @@ uint8array-base64
 # https://github.com/tc39/proposal-atomics-microwait
 Atomics.pause
 
+# Error.isError
+# https://github.com/tc39/proposal-is-error
+Error.isError
+
 ## Standard language features
 #
 # Language features that have been included in a published version of the

test/built-ins/Error/isError/bigints.js

@@ -5,7 +5,7 @@
 esid: sec-error.iserror
 description: >
   Returns false on bigints
-features: [BigInt]
+features: [Error.isError, BigInt]
 ---*/
 
 assert.sameValue(Error.isError(0n), false);

test/built-ins/Error/isError/error-subclass.js

@@ -5,7 +5,7 @@
 esid: sec-error.iserror
 description: >
   Returns true on userland Error subclasses
-features: [class]
+features: [Error.isError, class]
 ---*/
 
 class MyError extends Error {}

test/built-ins/Error/isError/errors-other-realm.js

@@ -5,7 +5,7 @@
 esid: sec-error.iserror
 description: >
   Returns true on Error and Error subclass instances from a different realm
-features: [cross-realm]
+features: [Error.isError, cross-realm]
 ---*/
 
 var other = $262.createRealm().global;

test/built-ins/Error/isError/errors.js

@@ -5,6 +5,7 @@
 esid: sec-error.iserror
 description: >
   Returns true on Error and Error subclass instances
+features: [Error.isError]
 ---*/
 
 assert.sameValue(Error.isError(new Error()), true);

test/built-ins/Error/isError/fake-errors.js

@@ -5,6 +5,7 @@
 esid: sec-error.iserror
 description: >
   Returns false on non-Error objects pretending to be an Error
+features: [Error.isError]
 ---*/
 
 var fakeError = {

test/built-ins/Error/isError/is-a-constructor.js

@@ -16,7 +16,7 @@ info: |
   If argument has a [[Construct]] internal method, return true.
   Return false.
 includes: [isConstructor.js]
-features: [Reflect.construct]
+features: [Error.isError, Reflect.construct]
 ---*/
 
 assert.sameValue(isConstructor(Error.isError), false, 'isConstructor(Error.isError) must return false');

test/built-ins/Error/isError/name.js

@@ -5,6 +5,7 @@
 esid: sec-error.iserror
 description: >
   The initial value of Error.isError.name is "isError".
+features: [Error.isError]
 ---*/
 
 assert.sameValue(Error.isError.name, 'isError');

test/built-ins/Error/isError/non-error-objects-other-realm.js

@@ -5,7 +5,7 @@
 esid: sec-error.iserror
 description: >
   Returns false on non-Error objects from a different realm
-features: [cross-realm]
+features: [Error.isError, cross-realm]
 ---*/
 
 var other = $262.createRealm().global;

test/built-ins/Error/isError/non-error-objects.js

@@ -5,6 +5,7 @@
 esid: sec-error.iserror
 description: >
   Returns false on non-Error objects
+features: [Error.isError]
 ---*/
 
 assert.sameValue(Error.isError({}), false);

test/built-ins/Error/isError/primitives.js

@@ -5,6 +5,7 @@
 esid: sec-error.iserror
 description: >
   Returns false on primitives
+features: [Error.isError]
 ---*/
 
 assert.sameValue(Error.isError(), false);

test/built-ins/Error/isError/prop-desc.js

@@ -9,6 +9,7 @@ info: |
   has the attributes { [[Writable]]: true, [[Enumerable]]: false,
   [[Configurable]]: true } unless otherwise specified.
 includes: [propertyHelper.js]
+features: [Error.isError]
 ---*/
 
 verifyProperty(Error, "isError", {

test/built-ins/Error/isError/symbols.js

@@ -5,7 +5,7 @@
 esid: sec-error.iserror
 description: >
   Returns false on symbols
-features: [Symbol]
+features: [Error.isError, Symbol]
 ---*/
 
 assert.sameValue(Error.isError(new Symbol()), false);