Codechange: rename str_validate to StrMakeValid(InPlace) (#9304)

This to be more explicit the function changes the value, and not
returns yes/no.

Codechange: move bits of SettingDesc down to the appropriate sub classes

And by doing so remove the hack where ints were put into pointers so "def" could either be an int or a string

Codechange: use initializer_lists for the settings tables

Not using vectors as those require copying from the initializer list and that
makes unique_ptrs to the actual SettingDesc objects later impossible.

Change: [Network] Update server's NetworkServerGameInfo only when needed

Split the updating in a "static" version that only needs to be called when a new map is loaded or some settings are changed, and a "dynamic" version that updates everything that changes regularly such as the current game date or the number of spectators.

Feature: setting to indicate snow coverage for arctic climate (replaces snow line height)

Setting the snow coverage (in % of the map) makes a lot more sense
to the human, while still allowing the niche player to set (by
finding the correct %) a snow line height they like. This makes for
easier defaults, as it decoupled terrain height from amount of snow.

Maps can never be 100% snow, as we do not have sprites for coastal
tiles.

Internally, this calculates the best snow line height to approach
this coverage as close as possible.

Add: save openttd.cfg immediately on changing a setting (#8358)

Formally it was only done on exit. This means that if it crashes
changes in settings were not stored. This is often rather
frustrating. Additionally, targets (like emscripten) where people
are unlike to use "Exit Game", will never see their configuration
stored.

The drawback is that on every setting change there is some minor
I/O of writing the ini file to disk again.

Add: [Win32] GDI engine for font glyph rendering as a replacement for including FreeType.

Building with FreeType is still possible and will take precedence over the GDI renderer, but
the project files don't include FreeType anymore by default. Combining GDI rendering with ICU
text layout is untested.

Codechange: Refactor the Freetype font cache into a generic part that does not depend on Freetype and into one that does.

This makes it easier to add other TrueType font rendering engines.

Remove: ENABLE_NETWORK switch

This switch has been a pain for years. Often disabling broke
compilation, as no developer compiles OpenTTD without, neither do
any of our official binaries.

Additionaly, it has grown so hugely in our codebase, that it
clearly shows that the current solution was a poor one. 350+
instances of "#ifdef ENABLE_NETWORK" were in the code, of which
only ~30 in the networking code itself. The rest were all around
the code to do the right thing, from GUI to NewGRF.

A more proper solution would be to stub all the functions, and
make sure the rest of the code can simply assume network is
available. This was also partially done, and most variables were
correct if networking was disabled. Despite that, often the #ifdefs
were still used.

With the recent removal of DOS, there is also no platform anymore
which we support where networking isn't working out-of-the-box.

All in all, it is time to remove the ENABLE_NETWORK switch. No
replacement is planned, but if you feel we really need this option,
we welcome any Pull Request which implements this in a way that
doesn't crawl through the code like this diff shows we used to.

Codechange: Convert saveload numbers to enum values.

(This was mostly achieved with a few in-place regexes)

Feature: Group liveries, and livery window usability enhancements. (#7108)

* Change: Replace checkbox in livery selection window with Default option in drop down selection.

This reduces clutter in the UI and allows for primary/secondary colours to independently follow the default scheme if desired.

* Feature: Add vehicle group liveries.