fix: add $set and $on methods in legacy compat mode

[dummdidumm]

People could've done bind:this and called instance methods on the component instance - a rare case, but not impossible. This shims $set and $on when in legacy compat mode. $destroy is never shimmed because you shouldn't manually destroy a component, ever, and there's no way to make that work in the new world.
closes #10420

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