Add: Install additional documentation files with the game

Also include it in Emscripten packages

Add: use breakpad to create crash.dmp on MacOS / Linux too (#11202)

Normally only the Windows platform could create a crash.dmp, making
analysing crash-reports from MacOS / Linux rather tricky.

Codechange: Remove Freetype bits on Win32/OSX. (#10960)

These platforms have their own specific font rendering.

Codechange: fmt (and std::format) do explicitly not support enums out-of-the-box

That it works for the version we have packaged it pure coincidence, as that is
one of the few versions that due to a bug allow it. So add the appropriate
template specialisations to support it out-of-the-box within OpenTTD.

Feature: drop ICU-lx in favour of directly interfacing with harfbuzz

This means we have RTL support again with ICU 58+. It makes use of:
- ICU for bidi-itemization
- ICU for script-itemization
- OpenTTD for style-itemization
- harfbuzz for shaping

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.

Change: rebrand 1.12.0 to 12.0

One question that keeps popping up: "when do we release 2.0?".
NewGRF will force that at least 1.16 will be 2.0, but to not wait
for this, let's drop the "1." and be for ever done with that
conversation.

We are following in the footstep of giants here.

Fix #9386: compilers failing to compile with LTO by using variants instead of new + unique_ptr

With std::variant all memory can be figured out at compile time, so the compiler needs to keep track of fewer elements. It also saves out a unique_ptr and its memory management, over a slight impact for resolving a setting.

Fix: don't link to OpenGL with SDL2 as backend; SDL2 dynamically loads it (#8745)

Although for developers this doesn't change anything, for our
linux-generic binary it changes everything. Without this, the
OpenGL dynamic library is dragged in as dependency, and as it
depends on X11, that will be dragged in too. This is not
something we prefer to have, as that won't run on as many
machines as it could.

SDL2 doesn't depend on OpenGL directly, as it tries to load it
in on runtime. If found, it would work in exactly the same way
as if we would link to OpenGL ourselves. As such, this is
the best of both worlds: our linux-generics have less linked
dependencies, and developers won't notice any difference.

As a side-effect, if someone uses linux-generic on a machine
that does not have any OpenGL package installed, it will
gracefully fall back to the default backend of SDL instead.

Feature: [Actions / CMake] support for generic linux builds (#8641)

These bundles can be opened on any "modern" Linux machine with
a driver that SDL2 supports.

Machines needs at least glibc 2.15, which was released 10 years ago.
It is build with CentOS 7 as base, and only assumes the following
libraries are available on the system:
- libc
- libdl
- libgcc_s
- libpthread
- librt
- libstdc++

All other libraries the game depends on are bundled together with
the game, so users don't need any library installed to use this
bundle. The downside of course is that this increases the binary
size a bit: 30 MiB of libraries are in this bundle.

RPATH is used to make ld-linux find the folder libraries are
stored in; however, system libraries are always used before these,
in the assumption libraries on the user system are more up-to-date.

Using -DOPTION_PACKAGE_DEPENDENCIES=ON switches on packaging
of libraries in the "lib" folder. This requires CMake 3.16 to
be installed; otherwise it will fail.

Fix: [Emscripten] compile with exceptions enabled, as our AIs depend on it

Also parts of the saveload code does, and some other places. This
does slow down builds, but for most computers this will not be
measurable. At least, the ones I had access to I could not find
a difference in FPS, mainly as that is heavily limited by the Hz
of the screens of the computer.

Either way, it is better to have a full functional game than a
fast one in my opinion

Add: support for emscripten (play-OpenTTD-in-the-browser)

Emscripten compiles to WASM, which can be loaded via
HTML / JavaScript. This allows you to play OpenTTD inside a
browser.

Co-authored-by: milek7 <me@milek7.pl>

Change: don't encourage the use of LZO

LZO was used before the first version we track in our version
control system, which dates back to Aug 2004. Somewhere before
that time a few savegames / scenarios exist which use LZO. No
other savegame / scenario does since then. Let's not encourage
people to install something that ancient.

There are no scenarios on BaNaNaS that require LZO.

Fix: set Mac deployment target

This silences an awful lot of warnings.

Add: create bundles via CPack

CPack works closely together with CMake to do the right thing in
terms of bundling (called 'package'). This generates all the
packaging we need, and some more.

Add: introduce CMake for project management

CMake works on all our supported platforms, like MSVC, Mingw, GCC,
Clang, and many more. It allows for a single way of doing things,
so no longer we need shell scripts and vbs scripts to work on all
our supported platforms.

Additionally, CMake allows to generate project files for like MSVC,
KDevelop, etc.

This heavily reduces the lines of code we need to support multiple
platforms from a project perspective.

Addtiionally, this heavily improves our detection of libraries, etc.