[clang] [HLSL] Add 6.2 SM on half availability for length intrinsic (PR #122337)

[Farzon Lotfi via cfe-commits]

farzonl wrote:

> Does this fix a test failure?

No failures.  We would need to have tests for all intrinsics that if its not SM 6.2 or greater uses of half would error, but we never did that for any of the other intrinsics so we should probably discuss what the test coverage should be and apply it broadly. 

https://github.com/llvm/llvm-project/pull/122337