Fix: TextfileWindow called virtual methods before constructor completed. (#11889)

SetStringParameters() was called during widget tree init in the constructor.

Calls within a constructor cannot call the derived classes methods. This would result in invalid data being passed to the string system, which could then crash.

Codechange: Replace mishmash of types for widget index with WidgetID.

Indices were stored as int, but often passed around as uint/uint8_t and casts.

Now they should all use WidgetID.

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: Rename some freetype things to fontcache.

The font cache supports more than just FreeType as a font provider, but still used freetype in some naming.

This now uses more suitable terms.

Fix: 'Cache' top and bottom lines of textfile viewer to avoid overdraw. (#9131)

* Fix: 'Cache' top and bottom lines of textfile viewer to avoid overdraw.

The text file viewer calculated the number of lines required to set the scrollbar, but did not retain this information, so this was recalculated on every draw operation. This includes overdrawing text outside the bounds of the current scroll position.

With this change the top and bottom lines for each line of text are remembered, and reflowing is avoided where possible. Text outside the current scroll bounds is not drawn.
Additionally the scroll interval is now based on text lines instead of pixel lines, which increases the text capacity depending on the font size.

* Fix: Limit text viewer to showing 64k lines.

Text files with more than 64k wrapped lines would exceed the scrollbar capacity and cause an assert. This is harder to reach now that the scrollbar counts lines instead of pixels.