[llvm] [TableGen] Improvements to Named operands in InstrInfoEmitter (PR #124960)

[Mariusz Sikora via llvm-commits]

mariusz-sikora-at-amd wrote:

Hi @jurahul ,
We are also using OPERAND_LAST in downstream branch and we noticed that it was/is accessing first element from next row in OperandMap 2dim table. Proposal: https://github.com/llvm/llvm-project/pull/125424

```
namespace llvm::AMDGPU::OpName {
enum {
  a16 = 0,
 ...
  OPERAND_LAST = 115,

int16_t getNamedOperandIdx(uint16_t Opcode, uint16_t NamedIdx) {
  static constexpr int8_t OperandMap[][115] = {
```

https://github.com/llvm/llvm-project/pull/124960