don't permit using CEF builds that will have encoding problems with slot saves; we assume UTF16 strings.

Be a bit stricter about the encoding used for slot saves to avoid slot corruption with certain high-unicode characters, such as .

If XDG_CURRENT_DESKTOP isn't set, getenv returns a `nullptr`.
Constructing a `std::string` from `nullptr` will throw an exception.
This prevents a crash when not using a DE, but zenity or kdialog is
installed regardless

(also fixes a typo where the fallthrough attribute wasn't applied to
anything due to a missing semicolon)

CEF requires C++11 and thus removed the OVERRIDE macro, requires using
nullptr instead of NULL.
Version 95 removed some settings:
https://bitbucket.org/chromiumembedded/cef/issues/2820/remove-cefbrowsersettings

CEF requires C++11 and thus removed the OVERRIDE macro, requires using
nullptr instead of NULL.
Version 95 removed some settings:
https://bitbucket.org/chromiumembedded/cef/issues/2820/remove-cefbrowsersettings

CefExecuteProcess needs the app pointer otherwise initialization in multi-process mode doesn't work correctly

where possible (everywhere except Windows) replace copying game file
with symlinking, on Linux do the same to CEF libraries.

Remove bundled CEF modules, leave only FindCEF for CEF_ROOT var
handling.

TRy to find system CEF module first.

Consolidate the general, platform-agnostic part of the main()/WinMain()
in static FCHost::main() function to avoid code duplication.

Linux handlers and main() were copied from the cefsimple test app,
persistent storage implementation rewritten using cstdio and
std::filesystem to make it cross-platform.

Hack a Javascript color picker into FC when it's loaded from FCHost, since we don't have a native one.

Current versions of CEF no longer support CefFrame::LoadString, so switch to a data-URI scheme instead

Probably ought to actually build the storage module, since it's pretty much the most important part of this whole thing.