Cleanup exception and error handling

[MrSmoke]

Breaking changes

Major

• 403 now throws a ForbiddenException instead of a UnauthorizedException
• Error.Body is now nullable

Minor

• Renamed TooManyRequestException to TooManyRequestsException
• Specific http client exceptions (such as BadRequestException) no longer accept a HttpStatusCode in the constructor

Changes

• Cleanup ErrorHelper.GetErrorException to simplify exception generation. All 1xx/2xx/3xx no longer throw any exceptions
• Updated ClickViewClientHttpException to have a nullable message
• Added new ForbiddenException which is now thrown on 403 responses
• Fix nullable warnings in QueryHelpers
• Removed GetDefaultErrorBody from BaseRestClientRequest
• Updated GetErrorAsync to set Error.Body to null if TryParseErrorBody did not parse an error body
• Added a default implementation of TryParseErrorBody which uses ReasonPhrase as the message (if set)
• Shim 429 status code and remove custom int cast in error handling logic