src: add fast path for equal size to Reallocate()

When old and new size match, we can skip the rest of the function,
which makes sense in the case of embedders who do not use Node's
allocator, as that would lead to needlessly allocating and freeing
buffers of identical sizes.

PR-URL: nodejs#26573
Reviewed-By: Colin Ihrig <cjihrig@gmail.com>
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: James M Snell <jasnell@gmail.com>

Author: addaleax

src/env.cc

@@ -859,6 +859,7 @@ void Environment::BuildEmbedderGraph(Isolate* isolate,
 }
 
 char* Environment::Reallocate(char* data, size_t old_size, size_t size) {
+  if (old_size == size) return data;
   // If we know that the allocator is our ArrayBufferAllocator, we can let
   // if reallocate directly.
   if (isolate_data()->uses_node_allocator()) {