T: Sized bounds on methods of T: ?Sized impls are omitted in the docs

[glandium]

There are not a lot of those around, according to a quick grep. The vast majority are in core::ptr. Anyways, in e.g. core::ptr, there is:

impl<T: ?Sized> *mut T {
    ...
    pub unsafe fn offset(self, count: isize) -> *const T where T: Sized {
        intrinsics::offset(self, count)
    }
    ....
}

Note that the impl has a T: ?Sized bound, but the offset method has an additional T: Sized bound.

But the corresponding doc says nothing about that bound:
https://doc.rust-lang.org/std/primitive.pointer.html#method.offset-1

which ends up being misleading, since the only bound shown on the page is T: ?Sized.

I hit a surprising

14 |         if ptr.is_null() {
   |                ^^^^^^^ `T` does not have a constant size known at compile-time
   |
   = help: the trait `core::marker::Sized` is not implemented for `T`
   = help: consider adding a `where T: core::marker::Sized` bound

because of that discrepancy (but didn't pick is_null above because it changed in beta/nightly, it doesn't have the T: Sized bound anymore ; offset still does)

[glandium]

duplicate of #24183