Add non-panicking variants of pow for integer types

[milesand]

Currently, calling pow may panic in case of overflow, and the function does not have non-panicking counterparts. Thus, it would be beneficial to add those in.

Closes #48291.
Relevant tracking issue: #48320

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[milesand]

Squashed and rebased.

[alexcrichton]

Thanks! Would it be possible perhaps to implement these methods in terms of one another? For example checked_pow can just call overflowing_pow, right?

[milesand]

It would be possible, though that might incur some performace penalty(haven't benchmarked, so not sure). checked_pow implemented with overflowing_pow, for instance, would lack early return on overflow. I'm not quite sure about other cases, though.

[alexcrichton]

Ah ok yeah that makes sense to me, the loop does indeed seem like it throws a wrench into performance here.

In that case...

@bors: r+

[bors]

📌 Commit b31ff95 has been approved by alexcrichton

[alexcrichton]

@bors: rollup