Userland: Convert TLS::TLSv12 to a Core::Stream::Socket

This commit converts TLS::TLSv12 to a Core::Stream object, and in the
process allows TLS to now wrap other Core::Stream::Socket objects.
As a large part of LibHTTP and LibGemini depend on LibTLS's interface,
this also converts those to support Core::Stream, which leads to a
simplification of LibHTTP (as there's no need to care about the
underlying socket type anymore).
Note that RequestServer now controls the TLS socket options, which is a
better place anyway, as RS is the first receiver of the user-requested
options (though this is currently not particularly useful).

Userland/Libraries/LibHTTP/HttpResponse.cpp

@@ -8,9 +8,10 @@
 
 namespace HTTP {
 
-HttpResponse::HttpResponse(int code, HashMap<String, String, CaseInsensitiveStringTraits>&& headers)
+HttpResponse::HttpResponse(int code, HashMap<String, String, CaseInsensitiveStringTraits>&& headers, size_t size)
     : m_code(code)
     , m_headers(move(headers))
+    , m_downloaded_size(size)
 {
 }