feat: add system time offset setting (#6139)

* Add setting for system time offset

Add a setting to displace citra system time by days, hours, minutes
or seconds
Add UI for the setting which is only visible when clock is set to
system time
Change core/settings.h to include the setting

* Add system time offset to kernel

Actually makes use of the time offset.

* Fix time offset calculatioon in core/movie.cpp

* Replace C++20 chrono::days with seconds

Hopefully fixes the build.

src/citra/config.cpp

@@ -242,6 +242,58 @@ void Config::ReadValues() {
                 .count();
     }
 
+    {
+        constexpr const char* default_init_time_offset = "0 00:00:00";
+
+        std::string offset_string =
+            sdl2_config->GetString("System", "init_time_offset", default_init_time_offset);
+
+        size_t sep_index = offset_string.find(' ');
+
+        if (sep_index == std::string::npos) {
+            LOG_ERROR(Config, "Failed to parse init_time_offset. Using 0 00:00:00");
+            offset_string = default_init_time_offset;
+
+            sep_index = offset_string.find(' ');
+        }
+
+        std::string day_string = offset_string.substr(0, sep_index);
+        long long days = 0;
+
+        try {
+            days = std::stoll(day_string);
+        } catch (std::exception& e) {
+            LOG_ERROR(Config, "Failed to parse days in init_time_offset. Using 0");
+            days = 0;
+        }
+
+        long long days_in_seconds = days * 86400;
+
+        std::tm t;
+        t.tm_sec = 0;
+        t.tm_min = 0;
+        t.tm_hour = 0;
+        t.tm_mday = 1;
+        t.tm_mon = 0;
+        t.tm_year = 100;
+        t.tm_isdst = 0;
+
+        std::istringstream string_stream(offset_string.substr(sep_index + 1));
+        string_stream >> std::get_time(&t, "%H:%M:%S");
+
+        if (string_stream.fail()) {
+            LOG_ERROR(Config,
+                      "Failed to parse hours, minutes and seconds in init_time_offset. 00:00:00");
+        }
+
+        auto time_offset =
+            std::chrono::system_clock::from_time_t(std::mktime(&t)).time_since_epoch();
+
+        auto secs = std::chrono::duration_cast<std::chrono::seconds>(time_offset).count();
+
+        Settings::values.init_time_offset = static_cast<long long>(secs) + days_in_seconds;
+    }
+
     // Camera
     using namespace Service::CAM;
     Settings::values.camera_name[OuterRightCamera] =