clientgen: fix panic when generation openapi with named unions

[fredr]

Reported in https://discord.com/channels/814482502336905216/1445923767015571599/1448428947607130183

type FooRequest = {
  foo: string;
};

type ApiRequest = {
  blob: FooRequest | string;
};

export const myApi = api<ApiRequest, void>(
  { expose: true, method: "POST" },
  (req) => {},
);

Now yields:

{
  "schema": {
    "properties": {
      "blob": {
        "anyOf": [
          {
            "$ref": "#/components/schemas/hello.FooRequest"
          },
          {
            "type": "string"
          }
        ]
      }
    },
    "required": [
      "blob"
    ],
    "type": "object"
  }
}

Possibly also solves #1757 #1521 #1867

[encore-cla]

All committers have signed the CLA.

[eleijonmarck]

looks valid to me

[eandre]

Does this change how the schema looks like? Does everything get nested as refs now?

[fredr]

Does this change how the schema looks like? Does everything get nested as refs now?

No, I tried to show that in the example, e.g string is represented as {"type": "string"} as before the change, but named will be represented as ref. Or where there any other types you where thinking about?