Simplify library dependencies on `compiler-builtins`
The three panic-related library crates need to have access to `core`, and `compiler-builtins` needs to be in the crate graph. Rather than specifying both dependencies, switch these crates to use `rustc-std-workspace-core` which already does this.
This means there is now a single place that the `compiler-builtins` dependency needs to get configured, for everything other than `alloc` and `std`.
The second commit removes `compiler-builtins` from `std` (more details in the message).
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