[llvm] [TableGen] Add support for sparse direct-lookup tables (PR #201158)

[Igor Wodiany via llvm-commits]

IgWod wrote:

>Does it need to be a whole new SparseTable class, or could it be implemented with some kind of option on GenericTable? Maybe TableGen could even choose intelligently between binary search and sparse direct lookup?

I thought it does, but I think if I can change how I generate VOPDX/VOPDY eligibility records I should be able to use `GenericTable`, then it'd be a matter of extending `GenericTable` to support sparsity. Let me work on it.

https://github.com/llvm/llvm-project/pull/201158