[C++] Removed most heap allocations in builder (#6620)

* [C++] Removed most heap allocations in builder

* Updated API docs to indicate heap usage

* Override assertion for heap allocation in parser

* Cleaned up implemenations, enable heap alloc for tests

* Generalized CreateVectorOfStrings

* remove cmake option for heap alloc. reverted two heap removals

* Only use scratch space for vector of strings

* Override Windows SCL warning

* Changed std::transform to for loop to avoid MSCV warnings

* switched to const iterators

include/flatbuffers/base.h

@@ -247,6 +247,11 @@ namespace flatbuffers {
   #endif // __has_include
 #endif // !FLATBUFFERS_HAS_STRING_VIEW
 
+#ifndef FLATBUFFERS_GENERAL_HEAP_ALLOC_OK
+  // Allow heap allocations to be used
+  #define FLATBUFFERS_GENERAL_HEAP_ALLOC_OK 1
+#endif // !FLATBUFFERS_GENERAL_HEAP_ALLOC_OK
+
 #ifndef FLATBUFFERS_HAS_NEW_STRTOD
   // Modern (C++11) strtod and strtof functions are available for use.
   // 1) nan/inf strings as argument of strtod;