eslint: Prohibit import cycles in TypeScript.

Signed-off-by: Anders Kaseorg <anders@zulip.com>

.eslintrc.json

@@ -193,6 +193,7 @@
                 "@typescript-eslint/prefer-string-starts-ends-with": "error",
                 "@typescript-eslint/promise-function-async": "error",
                 "@typescript-eslint/unified-signatures": "error",
+                "import/no-cycle": "error",
                 "no-undef": "error"
             }
         },