[common] pcl::getMinMax3d() support for pcl::PointXY

Describe the bug

i cannot create pcl::segmentation with pcl::PointXY , it have a default way to convert to Eigen vector 4 map
Context

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Expected behavior

it should be able to give you min max of x y points and 0 for z and w

Current Behavior

What happens instead of the expected behavior?
compilation issue
To Reproduce

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Screenshots/Code snippets

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Your Environment (please complete the following information):

• OS: [e.g. Ubuntu 16.04]
• Compiler: [:eg GCC 8.1]
• PCL Version [e.g. 1.10, HEAD]

Possible Solution

//////////////////////////////////////////////////////////////////////////
template <typename PointT> void
pcl::MaximumLikelihoodSampleConsensus<PointT>::getMinMax (
    const PointCloudConstPtr &cloud, 
    const IndicesPtr &indices,
    Eigen::Vector4f &min_p, 
    Eigen::Vector4f &max_p) const
{
  min_p.setConstant (std::numeric_limits<float>::max());
  max_p.setConstant (std::numeric_limits<float>::lowest());
  min_p[3] = max_p[3] = 0;

  for (std::size_t i = 0; i < indices->size (); ++i)
  {
    if ((*cloud)[(*indices)[i]].x < min_p[0]) min_p[0] = (*cloud)[(*indices)[i]].x;
    if ((*cloud)[(*indices)[i]].y < min_p[1]) min_p[1] = (*cloud)[(*indices)[i]].y;
    if ((*cloud)[(*indices)[i]].z < min_p[2]) min_p[2] = (*cloud)[(*indices)[i]].z;

    if ((*cloud)[(*indices)[i]].x > max_p[0]) max_p[0] = (*cloud)[(*indices)[i]].x;
    if ((*cloud)[(*indices)[i]].y > max_p[1]) max_p[1] = (*cloud)[(*indices)[i]].y;
    if ((*cloud)[(*indices)[i]].z > max_p[2]) max_p[2] = (*cloud)[(*indices)[i]].z;
  }
}

you can make this global common i cannot use it outside this class

all min max does not support the PointXY

Not obligatory, but suggest a fix/reason for the bug. Feel free to create a PR if you feel comfortable.

Additional context

Add any other context about the problem here.

Start by locating the common pcl::getMinMax3d() implementation and the pcl::PointXY type, then compare them with MaximumLikelihoodSampleConsensus::getMinMax shown in the issue. Reproduce the compilation failure with pcl::PointXY and segmentation, and consider the work done when min/max results provide x and y while z and w are zero.