Add repositoryId overloads to methods on I(Observable)PullRequestReviewCommentReactionsClient

[alexander-efremov]

As part of my work on #1120 I've added new overloads on I(Observable)PullRequestReviewCommentReactionsClient to get access by repository id.

• Update XML documentation of interface methods of clients (also synchronize XML docs of IPullRequestReviewCommentReactionsClient and IObservablePullRequestReviewCommentReactionsClient ).

  There is some divergence between XML documentation of methods in IPullRequestReviewCommentReactionsClient and IObservablePullRequestReviewCommentReactionsClient . So I've decided
  to sync XML documentation of these classes during my work on Add support for interacting with repositories by id. #1120.

• Add overloads to IPullRequestReviewCommentReactionsClient .

  Just add overloads of existing methods that use repositoryId to work with repo.

• Add overloads to IObservablePullRequestReviewCommentReactionsClient .

  Just add overloads of existing methods that use repositoryId to work with repo.

• Add unit tests.

  I've added new unit tests that use repositoryId to work with repo that is just a full copy of existing tests that use (owner, name) key.
  Also I've found out that not all methods are covered by tests and added them for new and for old methods.

• Add integration tests.

  I've added new integration tests that use repositoryId to work with repo that is just a full copy of existing tests that use (owner, name) key.
  I've deleted class ObservablePullRequestReviewCommentReactionsClient Tests beacuse it is useless. All test cases are covered in non-reactive PullRequestReviewCommentReactionsClient Tests class.

/cc @shiftkey, @ryangribble

[alexander-efremov]

I've cleared tags here.

[shiftkey]

Tests are good. Just need to remove the empty <returns></returns> elements.

[alexander-efremov]

@shiftkey done!