Allow backwards-compatible createSocket calls

[Sineaggi]

In order to allow for backwards-compatibility with projects that override/extend the existing plain and ssl connection factories, we'll specify the createSocket(Proxy, HttpContext) method to call the original createSocket method when proxy is null.

[ok2c]

@Sineaggi Also cherry-picked to 5.3.x

[Sineaggi]

@ok2c thanks!

[ok2c]

@Sineaggi I intend to deprecate the entire ConnectionSocketFactory layer that goes back to the days of HttpClient v2 and harmonize the TLS setup logic of the classic transport with the async one, possibly by providing a single TLS strategy that works with both transports. If you are interested in reviewing or collaborating on the new APIs do let me know.

[arturobernalg]

@Sineaggi I intend to deprecate the entire ConnectionSocketFactory layer that goes back to the days of HttpClient v2 and harmonize the TLS setup logic of the classic transport with the async one, possibly by providing a single TLS strategy that works with both transports. If you are interested in reviewing or collaborating on the new APIs do let me know.

@ok2c I'd be interested in collaborating on the new APIs and reviewing the harmonization of the TLS setup logic across transports.

[ok2c]

@ok2c I'd be interested in collaborating on the new APIs and reviewing the harmonization of the TLS setup logic across transports.

@arturobernalg Sure. The proposed changes will go through the standard review process.

[ok2c]

@Sineaggi Please see #540. Do feel free to let me know if you want anything done differently to ensure API compatibility with your specific application.