Clean up ty::Dynamic

[fmease]

1. As a follow-up to PR Remove support for dyn* from the compiler #143036, remove DynKind entirely.
2. Inside HIR ty lowering, consolidate modules dyn_compatibility and lint into dyn_trait
   • dyn_compatibility wasn't about dyn compatibility itself, it's about lowering trait object types
   • lint contained dyn-Trait-specific diagnostics+lints only

[rustbot]

This PR changes rustc_public

cc @oli-obk, @celinval, @ouz-a

Some changes occurred in compiler/rustc_sanitizers

cc @rcvalle

Some changes occurred to the CTFE machinery

cc @RalfJung, @oli-obk, @lcnr

changes to the core type system

cc @compiler-errors, @lcnr

Some changes occurred in src/tools/clippy

cc @rust-lang/clippy

Some changes occurred in compiler/rustc_codegen_ssa

cc @WaffleLapkin

Some changes occurred in compiler/rustc_codegen_cranelift

cc @bjorn3

Some changes occurred to the CTFE / Miri interpreter

cc @rust-lang/miri

Some changes occurred to MIR optimizations

cc @rust-lang/wg-mir-opt

Some changes occurred in exhaustiveness checking

cc @Nadrieril

[rustbot]

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