[release/6.0] [mini] Dynamically allocate a buffer for large runtime invoke results

[github-actions]

Backport of #58215 to release/6.0

/cc @lambdageek

Customer Impact

1. User programs on ios devices that use System.Text.Json to serialize large structs will crash.
2. Incorrect unsafe methods that return null from a ref-return method will crash instead of throwing a NullReferenceException.

Testing

CI and manual testing

Risk

Low. For (1) all the logic in the runtime is the same, we just dynamically allocate a big enough buffer. For (2) we already do the right thing when using LLVM AOT - this is just fixing up the non-LLVM AOT case.