Fix: race-condition when quitting the game with libcurl (#11688)

There could be a callback in _new_http_callbacks that is not
processed yet. All callbacks in _http_callbacks were cancelled,
but not the ones in _new_http_callbacks

Feature: opt-in survey when exiting a game

On first start-up, the game will ask if you want to participate
in our automated survey. You have to opt-in, and can easily opt-out
(via the Options) at any time.

When opt-in, whenever you exit a game, a JSON blob will be send
to the survey server hosted by OpenTTD. This JSON blob contains
information that gives a global picture of the game just played:
- What settings were used
- How many humans vs AIs
- How long the game has been played
- Basic information about the OS / CPU

All this information is kept very generic, so there is no
chance we send private information to our survey server.
Nothing in the JSON blob could identify you as a person; it
mostly tells about the game played. At any time you can see
what the JSON blob includes, by pressing the "Preview Survey
Results" button in-game.

Change: include fmt.h C++ headers in stdafx.h

This to prevent compilation issues between runs with and without precompiled
headers. Also remove the headers from the rest of the code base as they are
not needed there anymore, although they do relatively little harm.

Change: try to detect the CA file/path for CURL (#10481)

The default is given compile-time, not run-time. So libcurl is
of no use to us.

Current list is kindly borrowed from
https://go.dev/src/crypto/x509/root_linux.go

Codechange: move curl into a thread so simplify code (#10480)

With a thread, we can just run curl_easy_perform() and let CURL
and threads handle the blocking part.

With async solution there are too many things to keep track of,
and it makes "when to update the GUI" tricky. By using a thread
that all gets a lot simpler, as the game-thread and download-thread
run side-by-side.

This is similar to how the WinHttp backend already works.

Add: use https:// for content-service connections (#10448)

This requires the use of WinHTTP (for Windows) or libcurl (for all
others except Emscripten). Emscripten does not support http(s)
calls currently.

On Linux it requires ca-certificates to be installed, so the HTTPS
certificate can be validated. It is really likely this is installed
on any modern machine, as most connections these days are HTTPS.

(On MacOS and Windows the certificate store is filled by default)

Reminder: in case the http(s):// connection cannot be established,
OpenTTD falls back to a custom TCP-based connection to fetch the
content from the content-service. Emscripten will always do this.