RFR: 8300792: Refactor examples in java.net.http to use @snippet

[Darragh Clarke]

On Tue, 21 Feb 2023 15:53:37 GMT, Darragh Clarke <duke at openjdk.org> wrote:

> Refactored instances of `@code` to instead use `@snippet`.
> 
> I also spent some time looking into using external snippets to reference the existing files `JavadocExamples` and `WebSocketExample` though ultimately thought it was better to keep the docs pretty much as they had been with only a few small changes to formatting.

I checked this over vs the existing docs and made some small formatting changes while fixing those build errors from the last commit.

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PR: https://git.openjdk.org/jdk/pull/12692