* Convert simple files to TS

* Fix jest tests

* Rename saved_objects_client{.js => .ts}

* WIP saved_objects_client

* saved_objects repository{.js => .ts}

* includedFields support string[] for type paramater

* Repository/saved_objects_client -> TS

* Fix tests and dependencies

* Fix saved objects type errors and simplify

* saved_objects/index saved_objects/service/index -> ts

* Fix saved objects export test after switching to typed mock

* Workaround type error

* Revert "Workaround type error"

This reverts commit de3252267eb2e6bf56a5584d271b55a7afdc1c53.

* Correctly type Server.savedObjects.SaveObjectsClient constructor

* saved_objects/service/lib/index.{js -> ts}

* saved_objects/service/lib/scoped_client_provider{js -> ts}

* Typescriptify scoped_client_provider

* Fix x-pack jest imports

* Add lodash/internal/toPath typings to xpath

* Introduce SavedObjectsClientContract

We need a way to specify that injected dependencies should adhere to the
SavedObjectsClient "contract". We can't use the SavedObjectsClient class
itself since it contains the private _repository property which in TS is
included in the type signature of a class.

* Cleanup and simplify types

* Fix repository#delete should return {}

* Add SavedObjects repository test for uncovered bug

Test for a bug in our previous js implementation that can lead to data
corruption and data loss.

If a bulkGet request is made where one of the objects to fetch is of a type
that isn't allowed, the returned result will include documents which have the
incorrect id and type assigned. E.g. the data of an object with id '1' is
returned with id '2'. Saving '2' will incorrectly override it's data with that
of the data of object '1'.

* SavedObject.updated_at: string and unify saved_object / serializer types

* Cleanup

* Address code review feedback

* Don't mock errors helpers in SavedObjectsClient Mock

* Address CR feedback

* CR Feedback #2

* Add kibana-platform as code owners of Saved Objects

* Better typings for SavedObjectsClient.errors

* Use unknown as default for generic type request paramater

* Bump @types/elasticsearch

* Fix types for isForbiddenError

* Bump x-pack @types/elasticsearch