GlobalISel: Make LegalizerHelper primitives public

  /// Expose LegalizerInfo so the clients can re-use.

  const LegalizerInfo &getLegalizerInfo() const { return LI; }

private:

  /// Legalize a single operand \p OpIdx of the machine instruction \p MI as a

  /// Use by extending the operand's type to \p WideTy using the specified \p

  /// ExtOpcode for the extension instruction, and replacing the vreg of the

  /// original vector type, and replacing the vreg of the operand in place.

  void moreElementsVectorSrc(MachineInstr &MI, LLT MoreTy, unsigned OpIdx);

private:

  LegalizeResult

  widenScalarMergeValues(MachineInstr &MI, unsigned TypeIdx, LLT WideTy);

  LegalizeResult