Stabilize pointer byte offsets and is aligned

[WaffleLapkin]

This PR stabilizes pointer_byte_offsets, const_pointer_byte_offsets (tracking issue) and pointer_is_aligned (tracking issue) features. Blocked on FCPs (1, 2).

r? libs-api
(also someone cast wg-const-eval for use of #[rustc_allow_const_fn_unstable(ptr_metadata)])

Resolves #96283, #96284 and #56304

[rustbot]

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If this PR contains changes to any rust-lang/rust public library APIs then please comment with @rustbot label +T-libs-api -T-libs to tag it appropriately. If this PR contains changes to any unstable APIs please edit the PR description to add a link to the relevant API Change Proposal or create one if you haven't already. If you're unsure where your change falls no worries, just leave it as is and the reviewer will take a look and make a decision to forward on if necessary.

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[rust-highfive]

r? @m-ou-se

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[WaffleLapkin]

@rustbot label +T-libs-api -T-libs

[bors]

☔ The latest upstream changes (presumably #102051) made this pull request unmergeable. Please resolve the merge conflicts.

[WaffleLapkin]

Closing this since pointer_is_aligned is unlikely to be stabilized anytime soon; I'll open a separate PR for pointer_byte_offsets/const_pointer_byte_offsets once libs-api will start and complite the necessary FCP.