Updating OAuthClient API based on latest service swagger

[Jeffders]

Updated the TokenAPI.json swagger file, and generated (for the first time), the autorest clients and supporting classes for this swagger. Then I updated the tests and BotFrameworkAdapter to use these methods.

I ran the unit tests and also did manual testing against production DirectLine:
-GetToken
-SignIn flow (with and without the magic code)
-SignOut
-GetAadTokens

[coveralls]

Pull Request Test Coverage Report for Build 48449

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 46 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.01%) to 69.47%

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Files with Coverage Reduction	New Missed Lines	%
/libraries/Microsoft.Bot.Builder/BotFrameworkAdapter.cs	46	15.55%

Totals
Change from base Build 48226:	-0.01%
Covered Lines:	3527
Relevant Lines:	5077

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💛 - Coveralls

[cleemullins]

I don't understand the relationship between this class, the "Old" version of this class, and the Interface.

My understanding is that this is a Breaking Change, which we can't do. I believe this needs to be OAuthClient2, and the old one can have a "[Obsolete / Depricated] attribute added to it.

[cleemullins]

@Jeffders Hey Jeff, this looks like a great improvement. There are a few breaking changes I saw in there that I don't think we'll be able to take - I called out the ones I saw, but you'll have to go through with a very careful eye.

Also - do we need to port this back to SDK3? I think we only need it in V4, but as it's protocol changes I'm not clear.

[cleemullins]

I've followed up with @Jeffders to figure out what to do with this PR.