Improve indexed access relation check for nested indexed accesses on the source side

[Andarist]

fixes #60675

[jfet97]

I'm suggesting a nested test, something like:

type EventPayloads = {
    completeSprint: {
        automationId: string,
        spaceId: string,
    },
    sendMessage: {
        message: string,
    },
}

type Nested = {
    bar: {
        a: string,
    },
    baz: {
        b: string,
    },
}

type CompletedEvent<T extends keyof EventPayloads, Z extends keyof Nested> = {
    [E in T]: {
        type: E,
        payload: {
            [K in Z]: {
                other: string,
                nested: Nested[K]
            }
        }[Z],
        appName: string,
    }
}[T]

function overwriteAppName<U extends keyof EventPayloads, Z extends keyof Nested>(
    scheduled: CompletedEvent<U, Z>,
): CompletedEvent<U, Z> {
    const { appName, type, ...rest } = scheduled
    const { other, ...restrest } = rest.payload

    return {
      type,
      payload: {
          ...restrest,
          other,
      },
      appName: "test",
    }
}

Here restrest has type CompletedEvent<U, Z>["payload"]["nested"] on purpose, to check how it behaves when a double reduction would be needed, but everything seems to be fine. getReducedApparentType(objectType) takes care of it.

[Andarist]

thanks for the nested test case! :)