[clang] [llvm] Add a generator for Unicode properties. (PR #229072)

[Aaron Ballman via cfe-commits]

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+# Unicode Support
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AaronBallman wrote:

I think it makes sense to move to LLVM and name it `HowToBuildUnicodeTables.md` along with the other HowTo docs; WDYT?

https://github.com/llvm/llvm-project/pull/229072