Angular: feat(http): Support many types of body on Request/Response and all ConnectionBackend implementations

[jeffbcross]

These types should be supported by all backends, as much as each backend is technically capable of supporting:

• FormData (for request only)
• Blob
• Document (for response only)
• Text (String)
• JSON

TBD: ArrayBufferView/ArrayBuffer?

All expected response types should be able to be explicitly declared on the Request, so that they can be optimized by the underlying primitive (see #2609). Request body types won't be explicitly declared.

[robwormald]

This issue was moved to angular/http#75

[squadwuschel]

the moved Link was not found @robwormald

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