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

0 files changed, 0 insertions, 0 deletions