RFR: 8283544: HttpClient GET method adds Content-Length: 0 header [v3]

[Conor Cleary]

> **Issue**
> When using the `HttpClient.send()` to send a GET request created using the `HttpRequest.newBuilder()`, a `Content-length: 0` header is set. This behaviour causes issues with many services as a body related header is usually not expected to be included with a GET request. 
> 
> **Solution**
> `Http1Request.java` was modified so that when the request method is a GET, a `Content-length` header is not added to the request. However, if a developer chooses to include a body in a GET request (though it is generally considered bad practice), a `Content-length` header with the appropriate value will be added.

Conor Cleary has updated the pull request incrementally with one additional commit since the last revision:

  8283544: Moved test assertions out of HttpHandlers

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/8017/files
  - new: https://git.openjdk.java.net/jdk/pull/8017/files/cb02c76d..132c1f31

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=8017&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=8017&range=01-02

  Stats: 33 lines in 1 file changed: 11 ins; 4 del; 18 mod
  Patch: https://git.openjdk.java.net/jdk/pull/8017.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/8017/head:pull/8017

PR: https://git.openjdk.java.net/jdk/pull/8017