Generate a monomorphic version of .createReadOnly and .instantiate for each class model

[airhorns]

The VScode Deopt explorer showed that .createReadOnly inside the class model register function was getting deoptimized because it closes over too-wide a variety of klass variable references. We're closing over it so it is correct, but to v8, the callsite is still the same I guess, so it has to deoptimize to pull the right value for the closure! Same for .is and .instantiate -- these dynamically produced functions make a huge difference if they are re-eval'd for each class instead of defined dynamically.

Removing this deoptimization recovered a lot of the node 18 => node 21 performance gap for me! Not all of it. It also makes node 18 faster, but not by nearly as much.

On main on node 18

instantiating a small root x 3,105,456 ops/sec ±0.15% (100 runs sampled)
instantiating a large root x 6,289 ops/sec ±0.68% (99 runs sampled)
instantiating a large union x 803,839 ops/sec ±1.33% (98 runs sampled)
instantiating a diverse root x 881,149 ops/sec ±1.35% (99 runs sampled)

On main on node 21

instantiating a small root x 1,942,360 ops/sec ±0.75% (94 runs sampled)
instantiating a large root x 3,725 ops/sec ±1.61% (93 runs sampled)
instantiating a large union x 468,432 ops/sec ±1.57% (95 runs sampled)
instantiating a diverse root x 604,151 ops/sec ±0.19% (96 runs sampled)

On branch on node 18

instantiating a small root x 3,047,781 ops/sec ±0.30% (95 runs sampled)
instantiating a large root x 6,842 ops/sec ±2.48% (96 runs sampled)
instantiating a large union x 1,085,365 ops/sec ±1.45% (99 runs sampled)
instantiating a diverse root x 983,455 ops/sec ±1.39% (100 runs sampled)

On branch on node 21

instantiating a small root x 1,904,508 ops/sec ±0.52% (99 runs sampled)
instantiating a large root x 5,247 ops/sec ±0.29% (98 runs sampled)
instantiating a large union x 523,979 ops/sec ±1.31% (95 runs sampled)
instantiating a diverse root x 1,040,574 ops/sec ±1.07% (101 runs sampled)

[thegedge]

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