[Enhanced Http] Using GetHttpRequestDataAsync in enhanced http model

[satvu]

Discussed in #1534. We either need to make it very clear that using GetHttpRequestDataAsync is not a supported scenario or make sure it is in sync (i.e., return an HttpRequestData implementation backed by the HttpContext).

[satvu]

Initial design plans:

Do not support using GetHttpRequestDataAsync when asp.net integration is present. The error message will be logged and tracked, and if many users are trying out this scenario, we will consider supporting this.