fs: deprecate passing invalid types in fs.existsSync

doc/api/deprecations.md

@@ -3772,6 +3772,19 @@ It is recommended to use the `new` qualifier instead. This applies to all REPL c
 
 <!-- md-lint skip-deprecation DEP0186 -->
 
+### DEP0187: `fs.existsSync` never throw on invalid arguments
+
+<!-- YAML
+changes:
+  - version: REPLACEME
+    pr-url: https://github.com/nodejs/node/pull/55753
+    description: Documentation-only.
+-->
+
+Type: Documentation-only
+
+Passing invalid argument types is deprecated.
+
 [NIST SP 800-38D]: https://nvlpubs.nist.gov/nistpubs/Legacy/SP/nistspecialpublication800-38d.pdf
 [RFC 6066]: https://tools.ietf.org/html/rfc6066#section-3
 [RFC 8247 Section 2.4]: https://www.rfc-editor.org/rfc/rfc8247#section-2.4