Remove LRO PollUntilDoneInternal

[LarryOsterman]

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

• Every implementation of Azure::Core::Operation implements an almost identical PollUntilDoneInternal function:

      while (true)
      {
        // Poll will update the raw response.
        Poll(context);
        if (IsDone())
        {
          break;
        }
        std::this_thread::sleep_for(period);
      }

      return Azure::Response<Azure::Security::KeyVault::Keys::KeyVaultKey>(
          m_value, std::make_unique<Azure::Core::Http::RawResponse>(*m_rawResponse));

• The Azure::Core::Operation has separate overloads for APIs with and without a Context parameter rather than providing a defaulted context parameter.

Describe the solution you'd like

• Move most or all of the implementation of PollUntilDone to Azure::Core::Operation - especially the loop around polling.

• Add a defaulted Context parameter and remove the redundant method overloads.