cg_llvm: Consistently import llvm::Type and llvm::Value

[Zalathar]

We already have other modules that import these types and other types from llvm, so having the re-exports type_::Type and value::Value just distracts rust-analyzer and results in messier and less-consistent imports.

No functional change.

[rustbot]

Some changes occurred in compiler/rustc_codegen_llvm/src/builder/autodiff.rs

cc @ZuseZ4

[rustbot]

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