fix(cli): cdk context --reset <number> does not work (aws#10619)

*By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license*

Fixes aws#3033

packages/aws-cdk/lib/commands/context.ts

@@ -106,8 +106,8 @@ function keyByNumber(context: any, n: number) {
 /**
  * Return enumerated keys in a definitive order
  */
-function contextKeys(context: any) {
-  const keys = Object.keys(context);
+function contextKeys(context: Context): [number, string][] {
+  const keys = context.keys;
   keys.sort();
   return enumerate1(keys);
 }

packages/aws-cdk/test/commands/context-command.test.ts

@@ -23,3 +23,26 @@ test('context reset can remove a context key', async () => {
     baz: 'quux',
   });
 });
+
+test('context reset can remove a context key using number', async () => {
+  // GIVEN
+  const configuration = new Configuration();
+  configuration.context.set('foo', 'bar');
+  configuration.context.set('baz', 'quux');
+
+  expect(configuration.context.all).toEqual({
+    foo: 'bar',
+    baz: 'quux',
+  });
+
+  // WHEN
+  await realHandler({
+    configuration,
+    args: { reset: '1' },
+  } as any);
+
+  // THEN
+  expect(configuration.context.all).toEqual({
+    foo: 'bar',
+  });
+});