lib: specialize Clone of array IntoIter

[Paladynee]

This PR adds the TrivialClone specialization to the PolymorphicIter type, which array::IntoIter uses. I also added another coretest for the default case (already existing test catches the specialized one).

There are no unwinding concerns since TrivialClone means cloning = copying and we never call Clone::clone.

array:IntoIter is being used on a lot of places in both core and in user code, and array::IntoIter (nor does its users) override Clone often and just delegate to the inner type PolymorphicIter which does not yet do the TrivialClone specialization and is burdened by the iterator and unwind safety shenanigans for all types, so this PR should address some of that. This should in turn slightly reduce both stack usage and remove unwinding prologue/epilogue etc. from such functions and improve our -Cno-prepopulate-passes codegen too.

perf: https://godbolt.org/z/eTPjj3hP3

[rustbot]

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