[llvm] [TableGen][Decoder] Decode operands with zero width or all bits known (PR #156358)

[Sergei Barannikov via llvm-commits]

s-barannikov wrote:

Can I get an approval here? I've extracted most of the target-specific changes into separate PRs, and the ones that remain should be trivial.

https://github.com/llvm/llvm-project/pull/156358