Consolidate SpecialHeadersVisitor and the RequestClientIdHeaderVisitor

[jorgerangel-msft]

There is consolidation that can be done in both visitors to reduce code complexity. We should ensure existing tests pass, and both azure and unbranded libraries on the client plugin work as expected when we do this.

[JoshLove-msft]

It may not be possible to completely consolidate as the SpecialRequestHeaders depend on Azure types, whereas RequestClientIdHeaderVisitor is agnostic as it needs to be used in the plugin. We could instead move the other client request Id header functionality into ClientRequestIdHeaderVisitor.