[PORT] Adds support for buffered replies to skill dialog

[tomlm]

Port this change from botbuilder-dotnet/master branch:
microsoft/botbuilder-dotnet#3496

Fixes #3475

Changed projects

• Microsoft.Bot.Builder.Dialogs
• Microsoft.Bot.Builder
• integration
• Microsoft.Bot.Builder.Dialogs.Tests

[Kaiqb]

@gabog - should this be assigned to you?

[cleemullins]

@Kaiqb - This is in the JS Repo. I think we'll need John to do this.

[stevengum]

Closed via #1852