Refactor vm.Initialize into factory.New

[joshua-kim]

Currently, VM instances invoke Initialize after being created by New. We can just move all initialization into Factory's New instead of having lazy-initialization pattern to simplify code.

[joshua-kim]

First PR in this running story to remove CreateStaticHandlers, which is needed because we create a new instance of the VM and tear it down just to set up our static apis. https://github.com/ava-labs/avalanchego/pull/2589

[joshua-kim]

Next PR is to refactor the feature extension code out of the VM Manager, so we can guarantee that we're returning a concrete VM type. https://github.com/ava-labs/avalanchego/pull/2578

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