This unifies the settings APIs.
This also unifies the sync and async registration APIs, since the async
registration API did not support adding non-functions to the API table.
Some information in conf.example cannot be generated from
settingtypes.txt, moving it to a new file makes generating
conf.example while preserving that information easier.
Regenerate conf.example from settingtypes.txt.
It would complain that the value should be higher than the lower
bound, when it should be higher than or equal to the lower bound.
Similar issue for the upper bound.
Re-add documentation of noise parameter formats.
Re-add 'mgv5_np_ground' noise parameters in group format.
Both these were deleted through auto-generation of conf.example.
Add note to builtin/mainmenu/dlg_settings_advanced.lua that this
documentation must be preserved.
Avoids unreachable code linter warning by moving generation code
(of minetest.conf.example and settings_translation_file.cpp)
out of dlg_settings_advanced.
Due to passing the settings, also it avoids reading the settings file twice.
Instead of activating the code by changing the active if-clauses,
its activation is now done by uncommenting the loadfile() statement.
