Update RELEASES.md with missing deprecation notes.

[CDirkx]

Adds the following missing deprecation notes for the 1.52.0 release:

• Deprecation of RustcEncodable, RustcDecodable (Deprecate RustcEncodable and RustcDecodable. #83160)
• Deprecation of alloc::LayoutErr (Update LayoutError/LayoutErr stability attributes #81767)
• Fix the deprecation of intrinsics::drop_in_place and collections::Bound (Deprecate intrinsics::drop_in_place and collections::Bound, which accidentally weren't deprecated #82122)

[rust-highfive]

r? @Mark-Simulacrum

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[rust-highfive]

⚠️ Warning ⚠️

• Pull requests are usually filed against the master branch for this repo, but this one is against stable. Please double check that you specified the right target!

[CDirkx]

I don't know how complete the compatibility notes section is supposed to be, if any of these were intentionally omitted let me know.
Also this PR is against stable, is that the correct procedure? Or should I wait until master has the 1.52.0 release notes.

[Mark-Simulacrum]

cc @pietroalbini @XAMPPRocky

It probably makes sense to target master for this PR, as we try to keep the stable branch updated to the release and not some delta thereof. I don't think we expect to rebuild artifacts at this point.

I don't think compat notes is the right section for this, though, as these aren't breaking changes or even changes users should expect to need to change away from, just that it may be desirable. I don't think we generally include notes on all deprecations.

[CDirkx]

#81767 is the PR that adjusted the deprecation since to 1.52.0, but it might be more informative to link to #77691 which includes the FCP.

[CDirkx]

I looked through the earlier compatibility notes, sometimes deprecation is mentioned under "compatibility notes", sometimes under "library", and indeed most of the time not at all. The deprecations that are mentioned are generally changes that affect a large number of users, such as mem::uninitialized or Error::cause, so I don't think the changes in this PR qualify.

[Mark-Simulacrum]

Yeah, I think I'm going to go ahead and give this a close. I don't think these deprecations necessarily qualify and any affected users will directly be told by the compiler regardless.

[Mark-Simulacrum]

Thanks!

[XAMPPRocky]

I don't have an opinion on their inclusion. Though I do think we should try and occasionally remind people about the relnotes tag, because I bet some of these missing come from people forgetting or just not knowing about it.

@CDirkx Thank you for your PR!