Move MaybeUninit static methods to inherent methods

[SUPERCILEX]

Proposal

Problem statement

Based on this comment, the methods were added when making them inherent impls on arrays wasn't possible. This has presumably been fixed in the intervening years.

Motivation, use-cases

bar.foo() is easier to read than Namespace::foo(bar).

Solution sketches

• Tidy up maybe_uninit_as_bytes API rust#103128
• Tidy up maybe_uninit_write_slice API rust#103130
• Tidy up maybe_uninit_slice API rust#103131

[scottmcm]

nit: I think you mean "inherent" not "extension".

But because MaybeUninit isn't Deref, having these as inherent methods rather than associated functions (like they need to be on ManuallyDrop) sounds reasonable to me.

[SUPERCILEX]

Yup, thanks!