Bug in workers types generation logic

Ref: https://github.com/cloudflare/workerd/pull/3855#discussion_r2027280698

https://github.com/cloudflare/workerd/pull/3855 changed the constructor function of the `TextDecoder` class to include an additional `jsg::Lock&` argument as the first argument passed. When generating the types, the type generator ended up creating the definition so that both optional arguments ended up with the name `options`, causing typescript generation to fail. A manual override had to be used to produce the correct results.