SearchOptions.facetFilters type is too restrictive

[Elias Norrby]

As per the docs, SearchOptions.facetFilters can be a list with elements being a list of string | string[]:

index.search('', {
  facetFilters: [["author:Stephen King", "genre:Horror"], "publisher:Penguin"]
});

The currently exported type, however, requires all elements to be of the same type, i.e. either string or string[]:

  readonly facetFilters?: string | readonly string[] | ReadonlyArray<readonly string[]>;

Attempting to call client.search with an array of mixed contents results in this error:

 error TS2322: Type '(string | string[])[]' is not assignable to type 'string | readonly string[] | readonly (readonly string[])[]'.
  Type '(string | string[])[]' is not assignable to type 'readonly (readonly string[])[]'.
    Type 'string | string[]' is not assignable to type 'readonly string[]'.
      Type 'string' is not assignable to type 'readonly string[]'.

           { facetFilters: ['abc:123', ['def:456','one:two']] },