Add eslint rule to prevent Map.has call immediately before Map.delete

.eslint-plugin-local/tests/code-no-redundant-has-before-delete-test.ts

@@ -0,0 +1,38 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+export function testRedundantHasBeforeDelete() {
+	const m = new Map<string, number>();
+	const s = new Set<string>();
+
+	// Invalid cases
+	m.delete('key');
+
+	s.delete('key');
+
+	// Cases with else clause
+	if (!m.delete('key')) {
+		console.log('not found');
+	}
+
+	if (m.delete('key')) {
+		console.log('deleted');
+	} else {
+		console.log('not found');
+	}
+
+	// Valid cases
+	m.delete('key');
+	s.delete('key');
+
+	if (m.has('key')) {
+		console.log('deleting');
+		m.delete('key');
+	}
+
+	if (m.has('key')) {
+		m.delete('otherKey');
+	}
+}