minor improvements for debugging

* Info page: status of Serial (can be disconnected on new MCUs), and owner of RX/TX pins
* improved handling of Serial (don't write if not connected)
* added min available stack size to debug output (esp32 only)
* webserver show remaining stack size
* webserver: show string buffer usage

wled00/wled_server.cpp

@@ -364,6 +364,9 @@ void initServer()
   #endif
   server.on("/", HTTP_GET, [](AsyncWebServerRequest *request){
     USER_PRINTF("%s Client request %s\n", serverDescription, request->url().c_str()); //WLEDMM: want to see if client connects to wled, for netdebug also wants to know server
+    #ifdef ARDUINO_ARCH_ESP32
+    USER_PRINT(pcTaskGetTaskName(NULL)); USER_PRINT(F(" min free stack ")); USER_PRINTLN(uxTaskGetStackHighWaterMark(NULL));
+    #endif
     if (captivePortal(request)) return;
     serveIndexOrWelcome(request);
   });
@@ -551,6 +554,13 @@ void serveSettingsJS(AsyncWebServerRequest* request)
   strcat_P(buf,PSTR("function GetV(){var d=document;"));
   getSettingsJS(request, subPage, buf+strlen(buf));  // this may overflow by 35bytes!!! WLEDMM add request
   strcat_P(buf,PSTR("}"));
+
+  #ifdef ARDUINO_ARCH_ESP32
+    DEBUG_PRINT(F("ServeSettingsJS: "));
+    DEBUG_PRINT(pcTaskGetTaskName(NULL)); DEBUG_PRINT(F(" min free stack ")); DEBUG_PRINT(uxTaskGetStackHighWaterMark(NULL));
+    DEBUG_PRINTF(PSTR(" bytes.\tString buffer usage: %4d of %d bytes\n"), strlen(buf)+1, SETTINGS_STACK_BUF_SIZE+37);
+  #endif
+
   request->send(200, "application/javascript", buf);
 }