[mlir] Rename `GeneralizeOuterUnitDims{Un}PackOpPattern`s (#116439)
Renames:
* `GeneralizeOuterUnitDimsPackOpPattern`,
* `GeneralizeOuterUnitDimsUnPackOpPattern`,
as
* `DecomposeOuterUnitDimsPackOpPattern`,
* `DecomposeOuterUnitDimsUnPackOpPattern`,
respectively. The new name better describes the underlying
transformation.