Adds restxml protocol test around xml preamble, CDATA, escaped characters

[skotambkar]

Description of changes:

1. Adds few protocol test for rest xml deserializers to check behavior with xml preamble, comments, CDATA, white space, characters that need to be escaped are present in xml response body.
2. Adds test cases for white space, character escaping when serializing into xml request body.

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