Create utility mechanism for finding wave size dependent opcodes used to
manipulate exec/lane masks.

True16 Add OpSel when optimizing exec mask

True16 VOPCX have the opsel argument. Add it when we create these
instructions in SIOptimizeExecMasking.

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Co-authored-by: Matt Arsenault <arsenm2@gmail.com>

- Change InstrInfoEmitter to emit OpName as an enum class
  instead of an anonymous enum in the OpName namespace.
- This will help clearly distinguish between values that are 
  OpNames vs just operand indices and should help avoid
  bugs due to confusion between the two.
- Rename OpName::OPERAND_LAST to NUM_OPERAND_NAMES.
- Emit declaration of getOperandIdx() along with the OpName
  enum so it doesn't have to be repeated in various headers.
- Also updated AMDGPU, RISCV, and WebAssembly backends
  to conform to the new definition of OpName (mostly
  mechanical changes).

- Add `LiveIntervalsAnalysis`.
- Add `LiveIntervalsPrinterPass`.
- Use `LiveIntervalsWrapperPass` in legacy pass manager.
- Use `std::unique_ptr` instead of raw pointer for `LICalc`, so
destructor and default move constructor can handle it correctly.

This would be the last analysis required by `PHIElimination`.

This only converts the instances where all that is needed is to change
the variable type name.

Basically, anything that involves a function that LiveRegUnits does not
directly have was skipped to play it safe.

Reverts
https://github.com/llvm/llvm-project/commit/7a0e222a17058a311b69153d0b6f1b4459414778

This reverts commit 2a13422b8bcee449405e3ebff957b4020805f91c.

It was causing test failures on the expensive check builders.

During the SIOptimizeExecMasking pass, we try to form V_CMPX
instructions by detecting S_AND_SAVEEXEC and V_MOV instructions.
Generally, we require the input operand of the V_MOV, which is the input
operand to the to-be-formed V_CMPX, to be alive. This is forced by
clearing the kill flags on the operand after V_CMPX has been generated.

However, if we have a kill of a register set that contains said
register, this will not be detected by clearKillFlags.
With this change, possible additional kill-flag candidates will be
detected during the final call to findInstrBackwards and then, the kill
flag will be removed to keep all registers in the set alive.

Co-authored-by: Thomas Symalla <thomas.symalla@amd.com>