The Java implementation of getting the list of post-processing
shaders only looked in the Sys folder and not the User folder.
This could be fixed in the Java implementation, but it's
simpler to just call the C++ implementation instead.

A C compiler would very much be unable to build this code anyway.

EmulationActivity has an instance of Settings. If you go to
SettingsActivity from EmulationActivity and change some settings,
the changes get saved to disk, but EmulationActivity's Settings
instance still contains the old settings in its map of all
settings (assuming the EmulationActivity was not killed by the
system to save memory). Then, once you're done playing your
game and exit EmulationActivity, EmulationActivity calls
Settings.saveSettings. This call to saveSettings first overwrites
the entire INI file with its map of all settings (which is
outdated) in order to save any legacy settings that have changed
(which they haven't, since the GUI doesn't let you change legacy
settings while a game is running). Then, it asks the new config
system to write the most up-to-date values available for non-legacy
settings, which should make all the settings be up-to-date again.
The problem here is that the new config system would skip writing
to disk if no settings changes had been made since the last time
we asked it to write to disk (i.e. since SettingsActivity exited).

NB: Calling Settings.loadSettings in EmulationActivity.onResume
is not a working solution. I assume this is because
SettingsActivity saves its settings in onStop and not onPause.

The goal of this change is to make Config::Get(const Info<T>&)
fast so that we can use it in hot paths.

During emulation, when LocalGame has a value but CurrentRun
doesn't, we want to read from LocalGame, not CurrentRun. This
change exposes a LAYER_ACTIVE option that handles this correctly.

Now that PR 8975 is merged, we can finally add this without hacks.

https://bugs.dolphin-emu.org/issues/11605