Add thread-safe utilities to LLVMType to allow constructing llvm types in a multi...

Add thread-safe utilities to LLVMType to allow constructing llvm types in a multi-threaded environment. The LLVMContext is not thread-safe and directly constructing a raw llvm::Type can create situations where the LLVMContext is modified by multiple threads at the same time.

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PiperOrigin-RevId: 249526233