std: Move overflowing ops to inherent methods

[alexcrichton]

This commit migrates all of the methods on num::wrapping::OverflowingOps onto
inherent methods of the integer types. This also fills out some missing gaps in
the saturating and checked departments such as:

• saturating_mul
• checked_{neg,rem,shl,shr}

This is done in preparation for stabilization,

cc #27755

[rust-highfive]

r? @nikomatsakis

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[alexcrichton]

r? @aturon

Note that this doesn't deprecate the old wrappers, it just prepares everything for the upcoming "deprecation commit"

[aturon]

Hm, this might be slightly premature given discussion here. Let's wait for some overall consensus before landing this change.

[bors]

☔ The latest upstream changes (presumably #30434) made this pull request unmergeable. Please resolve the merge conflicts.

[aturon]

This comment isn't quite clear about what value is returned on overflow.

[aturon]

@alexcrichton There seems to be consensus around the issue, so I've reviewed the PR and left a few nits. Once these are resolved r=me.

[ollie27]

I wouldn't expect overflowing_neg to return true when given 0 for unsigned ints as -0 can be represented as an unsigned int: 0.

Also it looks like checked_neg is missing for unsigned ints.

[alexcrichton]

@ollie27 ah good point about negating 0!

@aturon I've updated with hopefully a clarification about shifting and overflow with the mask, although it may still be a little unclear as it's somewhat technical, what do you think?

[aturon]

@bors: r+

[bors]

📌 Commit 7eb7699 has been approved by aturon

[bors]

⌛ Testing commit 7eb7699 with merge 9f6917d...

[bors]

☀️ Test successful - auto-linux-32-nopt-t, auto-linux-32-opt, auto-linux-64-debug-opt, auto-linux-64-nopt-t, auto-linux-64-opt, auto-linux-64-x-android-t, auto-linux-cross-opt, auto-linux-musl-64-opt, auto-mac-32-opt, auto-mac-64-nopt-t, auto-mac-64-opt, auto-win-gnu-32-nopt-t, auto-win-gnu-32-opt, auto-win-gnu-64-nopt-t, auto-win-gnu-64-opt, auto-win-msvc-32-opt, auto-win-msvc-64-opt