Start eslint 9 migration

For #230339

Starts migrating to eslint 9. Everything runs but it produces a number of errors

.eslint-plugin-local/code-no-potentially-unsafe-disposables.ts

@@ -0,0 +1,37 @@
+/*---------------------------------------------------------------------------------------------
+ *  Copyright (c) Microsoft Corporation. All rights reserved.
+ *  Licensed under the MIT License. See License.txt in the project root for license information.
+ *--------------------------------------------------------------------------------------------*/
+
+import * as eslint from 'eslint';
+
+/**
+ * Checks for potentially unsafe usage of `DisposableStore` / `MutableDisposable`.
+ *
+ * These have been the source of leaks in the past.
+ */
+export = new class implements eslint.Rule.RuleModule {
+
+	create(context: eslint.Rule.RuleContext): eslint.Rule.RuleListener {
+		function checkVariableDeclaration(inNode: any) {
+			context.report({
+				node: inNode,
+				message: `Use const for 'DisposableStore' to avoid leaks by accidental reassignment.`
+			});
+		}
+
+		function checkProperty(inNode: any) {
+			context.report({
+				node: inNode,
+				message: `Use readonly for DisposableStore/MutableDisposable to avoid leaks through accidental reassignment.`
+			});
+		}
+
+		return {
+			'VariableDeclaration[kind!="const"] NewExpression[callee.name="DisposableStore"]': checkVariableDeclaration,
+
+			'PropertyDefinition[readonly!=true][typeAnnotation.typeAnnotation.typeName.name=/DisposableStore|MutableDisposable/]': checkProperty,
+			'PropertyDefinition[readonly!=true] NewExpression[callee.name=/DisposableStore|MutableDisposable/]': checkProperty,
+		};
+	}
+};