Stabilize the supertrait_item_shadowing feature

[Amanieu]

Tracking issue: #89151

As per the lang team decision, this also sets the default lint levels as follows:

• supertrait_item_shadowing_definition warns by default.
• supertrait_item_shadowing_usage is allowed by default.

[rustbot]

The Miri subtree was changed

cc @rust-lang/miri

compiler-builtins is developed in its own repository. If possible, consider making this change to rust-lang/compiler-builtins instead.

cc @tgross35

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri, @RalfJung, @oli-obk, @lcnr

[rustbot]

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[traviscross]

Thanks @Amanieu for the stabilization PR. As you fill out the stabilization report for us, have a look at our stabilization report template:

https://rustc-dev-guide.rust-lang.org/stabilization_report_template.html#stabilization-report

[rustbot]

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy