Disable and trim 'Marshaler<T>' on Native AOT

[Sergio0694]

This type is super cursed and causes a ton of code to be rooted. It's also not really needed anymore on Native AOT. This PR makes its static constructor throw right away on Native AOT, allowing all its code to be removed. This should save a fair amount 🤞

[dongle-the-gadget]

Should we make this pay-for-play instead (using a feature flag, for instance) rather than a complete breaking change?

[Sergio0694]

@dongle-the-gadget there's two considerations for why we're not doing that:

• There should be no "play" here. Things should just keep working the same, because pretty much all marshalling code paths that used to rely on Marshaler<T> now rely on generated code from the AOT generator. Those who don't, we should just fix.
• Disabling this makes us add proper AOT annotations, so we get diagnostics to further help enforce not using them.

[manodasanW]

I need to double check what our behavior here is today when boxed arrays are marshaled from native side.

[Sergio0694]

This type should never be used on AOT (I left some comments above the type explaining it). Unless I'm missing some way it could still somehow end up being referenced on NAOT? I couldn't find any possible entry points though 🤔