src: remove extra heap allocation in GetSession()

Don't allocate + copy + free; allocate and fill in place, then hand off
the pointer to Buffer::New().

Avoids unnecessary heap allocations in the following methods:

- crypto.CryptoStream#getSession()
- tls.TLSSocket#getSession()

PR-URL: https://github.com/nodejs/node/pull/14122
Reviewed-By: Anna Henningsen <anna@addaleax.net>
Reviewed-By: James M Snell <jasnell@gmail.com>

src/node_crypto.cc

@@ -1804,11 +1804,10 @@ void SSLWrap<Base>::GetSession(const FunctionCallbackInfo<Value>& args) {
   int slen = i2d_SSL_SESSION(sess, nullptr);
   CHECK_GT(slen, 0);
 
-  char* sbuf = new char[slen];
+  char* sbuf = Malloc(slen);
   unsigned char* p = reinterpret_cast<unsigned char*>(sbuf);
   i2d_SSL_SESSION(sess, &p);
-  args.GetReturnValue().Set(Encode(env->isolate(), sbuf, slen, BUFFER));
+  args.GetReturnValue().Set(Buffer::New(env, sbuf, slen).ToLocalChecked());
-  delete[] sbuf;
 }