### Motivation:
- The properties that store the request body length and the cumulative number of bytes sent as part of a request are of type `Int`.
- On 32-bit devices, when sending requests larger than `Int32.max`, these properties overflow and cause a crash.
- To solve this problem, the properties should use the explicit `Int64` type.
### Modifications:
- Changed the type of the `known` field of the `RequestBodyLength` enum to `Int64`.
- Changed the type of `expectedBodyLength` and `sentBodyBytes` in `HTTPRequestStateMachine` to `Int64?` and `Int64` respectively.
- Deprecated the `public var length: Int?` property of `HTTPClient.Body` and backed it with a new property: `contentLength: Int64?`
- Added a new initializer and "overloaded" the `stream` function in `HTTPClient.Body` to work with the new `contentLength` property.
- **Note:** The newly added `stream` function has different parameter names (`length` -> `contentLength` and `stream` -> `bodyStream`) to avoid ambiguity problems.
- Added a test case that streams a 3GB request -- verified this fails with the types of the properties set explicitly to `Int32`.
### Result:
- 32-bit devices can send requests larger than 2GB without integer overflow issues.
aryan-25
David Nadoba