Lots of the code/structure was based off `AMDGPUCombinerHelper`,
`AMDGPUPreLegalizerCombiner`, etc.
Tasks completed:
- Create new `SPIRVCombinerHelper` inheriting from `CombinerHelper`
- Move combiner logic in `SPIRVPreLegalizerCombiner` to helper methods
in `SPIRVCombinerHelper`
- Update `SPIRVPreLegalizerCombiner` to use the new helper class
- Simplify `applySPIRVDistance` code
