[WASM] improve error logging

Summary: Emscripten instead of errors returns to JS pointer to error. To get meaningful message we need to pass this pointer back to C++, read value from it and return `error.what()` as string.

Test Plan:
1. Add this code `auto x =  SQLiteQueryExecutor::getStorage().get<Draft>("123");` and check if error from `ORM` is visible:
{F985698}
2. Add this code `throw std::runtime_error("TEST ERROR");` and check if error is visible:
{F985697}
3. Use null pointer
4. User not existing pointer

Reviewers: tomek, michal, marcin

Reviewed By: tomek

Subscribers: ashoat

Differential Revision: https://phab.comm.dev/D10396

web/cpp/SQLiteQueryExecutorBindings.cpp

@@ -8,7 +8,21 @@ namespace comm {
 
 using namespace emscripten;
 
+std::string getExceptionMessage(int exceptionPtr) {
+  if (exceptionPtr == 0) {
+    return std::string("Exception pointer value was null");
+  }
+
+  std::exception *e = reinterpret_cast<std::exception *>(exceptionPtr);
+  if (e) {
+    return std::string(e->what());
+  }
+  return std::string("Pointer to exception was invalid");
+}
+
 EMSCRIPTEN_BINDINGS(SQLiteQueryExecutor) {
+  function("getExceptionMessage", &getExceptionMessage);
+
   value_object<NullableString>("NullableString")
       .field("value", &NullableString::value)
       .field("isNull", &NullableString::isNull);