Champion: numeric IntPtr

# numeric IntPtr

## Summary
[summary]: #summary

`System.IntPtr` and `System.UIntPtr` become numeric types, aliased by `nint` and `nuint`, and gain the built-in status of `nint` and `nuint`.

## Motivation
[motivation]: #motivation

As part of numerics work for .NET 7, `System.IntPtr` and `System.UIntPtr` are becoming proper numeric types.
So the distinction between native integer types and their underlying types becomes unnecessary.

## Detailed design
[design]: #detailed-design

https://github.com/dotnet/csharplang/blob/main/proposals/csharp-11.0/numeric-intptr.md

## Drawbacks
[drawbacks]: #drawbacks

## Alternatives
[alternatives]: #alternatives

## Unresolved questions
[unresolved]: #unresolved-questions

## Design meetings

* https://github.com/dotnet/csharplang/blob/main/meetings/2022/LDM-2022-05-09.md#numeric-intptr