feat: Support all current timezones for GPS (#3406)

* Support all current timezones.

* Fix function name and calculation for timezone offset.

* Allow setting any time offset value from -12 to +14 in 15 minutes increments.

* Alternate timezone editor in Companion (from elecpower).

* Fix compiler warning.

* chore: Add the T20

radio/src/telemetry/spektrum.cpp

@@ -934,7 +934,7 @@ static void adjustTimeFromUTC(uint8_t hour, uint8_t min, uint8_t sec,
                               struct gtm *tp)
 {
   // Get current UTC date/time
-  __offtime(&g_rtcTime, -g_eeGeneral.timezone * 3600, tp);
+  __offtime(&g_rtcTime, -timezoneOffsetSeconds(g_eeGeneral.timezone, g_eeGeneral.timezoneMinutes), tp);
 
   tp->tm_hour = hour;
   tp->tm_min = min;