Deprecate orderings string values

[angeloashmore]

Is your feature request related to a problem? Please describe.

The orderings option allows for sorting query results. The client currently accepts a string in the format expected by Prismic's Rest API or an object describing a sorting.

String:

{
  orderings: "[my.product.price desc]"
}

Object:

{
  orderings: [
    { field: "my.product.price", direction: "desc" }
  ]
}

The second option is clearer to read, is typed via TypeScript, and shows that multiple orderings can be provided (as a result of it being an array).

The first option is easy to write incorrectly, provides no compile-time checks, and requires learning a new syntax.

Describe the solution you'd like

Deprecate string values for the orderings option and only allow the object version.

Additionally, orderings currently accepts a single value or an array. The type should be changed to only accept an array.

Describe alternatives you've considered

None :)

Additional context

This request was prompted by this Prismic Community question: https://community.prismic.io/t/how-to-sort-prismic-data-by-name-or-any-other-field/11793

[lihbr]

Closed in #279