[llvm] [llvm-c] Add C API methods to match size_t ConstantDataArray C++ API signatures (PR #84433)

[Quentin Dian via llvm-commits]

https://github.com/DianQK approved this pull request.

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I can merge this PR later, but would you mind making the email publicly available?

https://github.com/llvm/llvm-project/pull/84433