Improve the ABI between the panic runtime and libstd

[bjorn3]

• Use the Rust ABI rather than C ABI
• Mark some extern functions as safe
• Move PanicPayload from libcore to liballoc and directly reference Box<dyn Any> instead of *mut dyn Any
• Avoid an unnecessary allocation with panic=abort

Follow up to #160440

[rustbot]

r? @clarfonthey

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The reviewer was selected based on:

• Owners of files modified in this PR: libs
• libs expanded to 12 candidates
• Random selection from JohnTitor, Mark-Simulacrum, clarfonthey, nia-e

[rustbot]

This PR was rebased onto a different main commit. Here's a range-diff highlighting what actually changed.

Rebasing is a normal part of keeping PRs up to date, so no action is needed—this note is just to help reviewers.

[bjorn3]

#160440 has been merged, so this is ready for review.