Revert #11993: new number format system does not and cannot work for CJK languages

There are too many intricacies that I am unaware of that are popping up after
asking whether things are right or not.
I do not want to keep playing whack-a-mole, so just revert the whole thing.

This reverts:
15be383b934dbf7c876b6d6ffaec7a406c82a39f
360fe8b0b639be9d39bc03a9d5d34123204c14fa
1aa9a5c0abaf9c5d6c49a3a76e2b1d7134c0bd10
59f56941e50bd4ebad31f9e771a4441f647692e5
7e2eefb91ff5999667752eea6e13bd8a0d293f48
b741b2ba6f790891961cb66a9320e75ca168cee4
609d0071d5e6b93aa61688714e9b92cf102e4683
9f8fd80112c188675179c9568a9be84da3df1713
a253205b932cc50fc9f25be390a6aaa370f89a45
819c6c756edd68599571eae126f305d6e3d247fc

Codechange: split settings.ini over several files (#9421)

This reduced the load on compilers, as currently for example MacOS
doesn't like the huge settings-tables.

Additionally, nobody can find settings, as the list is massive and
unordered. By splitting it, it becomes a little bit more sensible.

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.

Codechange: merge guiflags and flags in settings .ini files

It was rather confusing which one was for what, especially as some
SaveLoad flags were settings-only. Clean up this mess a bit by
having only Setting flags.

Codechange: rename SettingGuiFlag to SettingFlag (#9332)

It is a lovely organicly grown enum, where it started off with
GUI-only flags, and after that a few flags got added that can be
considered GUI-only (the GUI disables/enables based on them), to
only have flags added that has nothing to do with the GUI.

So be less confusing, and rename them to what they do.

Additionally, I took this opportunity to rename 0ISDISABLED to
reflect what it really does.