Add Lua getUsage() function that returns percent of already used up i… (#5313)

* Add Lua getUsage() function that returns percent of already used up instructions in current script execution cycle. It can be used to avoid script being killed when doing long lasting tasks (like telemetry logs loading and parsing)

* Compilation fixes

* Doc fix

* Disable Lua script instructions limit in DEBUG mode

radio/src/lua/api_general.cpp

@@ -1171,6 +1171,21 @@ static int luaLoadScript(lua_State * L)
   }
 }
 
+/*luadoc
+@function getUsage()
+
+Get percent of already used Lua instructions in current script execution cycle.
+
+@retval usage (number) a value from 0 to 100 (percent)
+
+@status current Introduced in 2.2.1
+*/
+static int luaGetUsage(lua_State * L)
+{
+  lua_pushinteger(L, instructionsPercent);
+  return 1;
+}
+
 const luaL_Reg opentxLib[] = {
   { "getTime", luaGetTime },
   { "getDateTime", luaGetDateTime },
@@ -1193,6 +1208,7 @@ const luaL_Reg opentxLib[] = {
   { "getRSSI", luaGetRSSI },
   { "killEvents", luaKillEvents },
   { "loadScript", luaLoadScript },
+  { "getUsage", luaGetUsage },
 #if LCD_DEPTH > 1 && !defined(COLORLCD)
   { "GREY", luaGrey },
 #endif