Support Ids in MultiTermVectors API

[russcam]

This commit adds support for providing a set of Ids to MultiTermVectors API to be used in
conjunction with index and type provided in the URI.

Index() and Type() methods added to MultiTermVectorOperation to allow the default typeof(T)
values to be overidden.

Closes #3219

[codebrain]

Balmer-object orientation.

[russcam]

I thought about providing overloads for string, long, Guid, etc. much like the existing GetMany<T>(...).

[codebrain]

Could be useful, but easy to add later :)

[russcam]

that's what I err'ed on!

[codebrain]

And.OnlyContain... nice!

[codebrain]

Just out of curiosity, is there any reason why we .ToList() on setters like this; other than to force the execution of the IEnumerable at this point? Seems like we could save some allocations in these instances...

[russcam]

I don't know about this specific case, but in general would be to force execution as you say.

[russcam]

What is unusual with respect to the general API design in NEST, is that GetMany<T>(..) is additive rather than assignative to the operations. I understand why this is, and it's not the only place where a method call is additive

[codebrain]

@Mpdreamz - would be able to offer any insight?

[Mpdreamz]

Places where we are additive is AFAIK only in the bulk related API helpers since you can IndexMany and then IndexMany<Y> afterwards in a single bulk. That was the rationale behind the deviation. Definitely up for further discussion 😄

[codebrain]

Changes look good. ++ on documentation. Minor question raised on the .ToList() setter, but its a common pattern already, so no need to hold back the code for this.

[Mpdreamz]

build seed:58181 test "multitermvectorsids fails with:

   Tests.Document.Multiple.MultiTermVectors.MultiTermVectorsIdsApiTests.SerializesInitializer [FAIL]
      Expected True because RoundTrip: 0 itteration
      Deserialization has result: False
      RoundTripResult`1 success: False
      This is the first time I am serializing
        {
          "ids": [
      -     {},
      -     {}
      +     1001,
      +     1002
          ]
        }
      
       C# approximation of actual ------ 
       new {
        ids = new [] {
          1001,
          1002
        }
      };
       C# approximation of expected ------ 
       new {
        ids = new [] {
          {},
          {}
        }
      };, but found False.
      Stack Trace:
           at FluentAssertions.Execution.XUnit2TestFramework.Throw(String message)
           at FluentAssertions.Execution.AssertionScope.FailWith(String message, Object[] args)
           at FluentAssertions.Primitives.BooleanAssertions.BeTrue(String because, Object[] becauseArgs)
        C:\projects\elasticsearch-net\src\Tests\Tests.Core\Extensions\SerializationTesterAssertionExtensions.cs(9,0): at Tests.Core.Extensions.SerializationTesterAssertionExtensions.ShouldBeValid(SerializationResult result, String message)
        C:\projects\elasticsearch-net\src\Tests\Tests.Core\Extensions\SerializationTesterAssertionExtensions.cs(33,0): at Tests.Core.Extensions.SerializationTesterAssertionExtensions.AssertSerialize[T](SerializationTester tester, T object, Object expectedJson, String message, Boolean preserveNullInExpected)
        C:\projects\elasticsearch-net\src\Tests\Tests.Core\Serialization\ExpectJsonTestBase.cs(24,0): at Tests.Core.Serialization.ExpectJsonTestBase.RoundTripsOrSerializes[T](T object)
        C:\projects\elasticsearch-net\src\Tests\Tests\Framework\EndpointTests\ApiTestBase.cs(37,0): at Tests.Framework.ApiTestBase`5.SerializesInitializer()
    Tests.Document.Multiple.MultiTermVectors.MultiTermVectorsIdsApiTests.SerializesFluent [FAIL]
      Expected True because RoundTrip: 0 itteration
      Deserialization has result: False
      RoundTripResult`1 success: False
      This is the first time I am serializing
        {
          "ids": [
      -     {},
      -     {}
      +     1001,
      +     1002
          ]
        }
      
       C# approximation of actual ------ 
       new {
        ids = new [] {
          1001,
          1002
        }
      };
       C# approximation of expected ------ 
       new {
        ids = new [] {
          {},
          {}
        }
      };, but found False.