Use MTPROTO-over-TCP for HTTP proxy

[Fangliding]

Is your feature request related to a problem?

I think this is indeed a problem

Describe the solution you'd like

When using HTTP proxy in tdesktop, it only attempts to send data using the plain HTTP method (POST), which generates a huge number of connections (approximately several per second) that are not friendly to many proxies
But when using socks, it will only open a few TCP relays normally and transmit within them
HTTP proxy also supports direct relay of TCP (using CONNECT method), which can improve the efficiency of the proxy

Describe alternatives you've considered

The solution is very obvious, there is no alternatives :)

Additional context

I have read the mtp protocol and I think the HTTP transport is designed to adapt to the browser's request/response HTTP model, which is unnecessary on tdesktop

[ilya-fedin]

http/socks proxy support is done by qt, not tdesktop

[Fangliding]

http/socks proxy support is done by qt, not tdesktop

I think the problem is here

tdesktop/Telegram/SourceFiles/mtproto/session.cpp

Line 244 in 4505a2b

const auto useTcp = (proxyType != ProxyData::Type::Http);

It disabled TCP when using HTTP proxy

[ilya-fedin]

Can you rephrase the title as "Use MTPROTO-over-TCP for HTTP proxy"?