Use direct pointers as Type IDs (#2745)

Instead of using indices into the global interned type table. This
means that a lock is *never* needed to access an expanded Type. The
Type lock is now only acquired when a complex Type is created. On a
real-world wasm2js workload this improves wall clock time by 23% on my
machine with 72 cores and makes traffic on the Type lock entirely
insignificant.

**Before**

72 cores
real    0m6.914s
user    184.014s
sys     0m3.995s

1 core
real    0m25.903s
user    0m25.658s
sys     0m0.253s

**After**

72 cores
real    5.349s
user    70.309s
sys     9.691s

1 core
real    25.859s
user    25.615s
sys     0.253s

1 files changed, 1 insertions, 0 deletions

diff --git a/test/binaryen.js/pass-arguments.js.txt b/test/binaryen.js/pass-arguments.js.txt
index f877b2248..df98df08c 100644
--- a/test/binaryen.js/pass-arguments.js.txt
+++ b/test/binaryen.js/pass-arguments.js.txt
@@ -3,6 +3,7 @@
 #include <map>
 #include "binaryen-c.h"
 int main() {
+  std::map<size_t, BinaryenType> types;
   std::map<size_t, BinaryenExpressionRef> expressions;
   std::map<size_t, BinaryenFunctionRef> functions;
   std::map<size_t, BinaryenGlobalRef> globals;