Single json buffer (#2336)

* Single/static JSON buffer for all requests.

* Missing json.cpp changes.

* Async fix.

* Added conditional compile (WLED_USE_DYNAMIC_JSON).

* Advanced locking with time-out.

* Missing releaseJSONBufferLock() on error response.

* Fix for config saving.

* Fixes and optimisations.
Dadded debugging information.

* Fix for ledmaps.

* No unsolicited serial sending if GPIO1 allocated

* Stray semicolons

* Fix JSON ledmap

Co-authored-by: Blaz Kristan <blaz@kristan-sp.si>

wled00/util.cpp

@@ -0,0 +1,33 @@
+#include "wled.h"
+#include "fcn_declare.h"
+#include "const.h"
+
+//threading/network callback details: https://github.com/Aircoookie/WLED/pull/2336#discussion_r762276994
+bool requestJSONBufferLock(uint8_t module)
+{
+  unsigned long now = millis();
+
+  while (jsonBufferLock && millis()-now < 1000) delay(1); // wait for a second for buffer lock
+
+  if (millis()-now >= 1000) {
+    DEBUG_PRINT(F("ERROR: Locking JSON buffer failed! ("));
+    DEBUG_PRINT(jsonBufferLock);
+    DEBUG_PRINTLN(")");
+    return false; // waiting time-outed
+  }
+
+  jsonBufferLock = module ? module : 255;
+  fileDoc = &doc;  // used for applying presets (presets.cpp)
+  doc.clear();
+  return true;
+}
+
+
+void releaseJSONBufferLock()
+{
+  DEBUG_PRINT(F("JSON buffer released. ("));
+  DEBUG_PRINT(jsonBufferLock);
+  DEBUG_PRINTLN(")");
+  fileDoc = nullptr;
+  jsonBufferLock = 0;
+}