[filters] `Pyramid<RGB>::compute()` is broken

[ 17%] Building CXX object filters/CMakeFiles/pcl_filters.dir/src/pyramid.cpp.o
In file included from /__w/1/s/filters/include/pcl/filters/impl/pyramid.hpp:43:0,
                 from /__w/1/s/filters/include/pcl/filters/pyramid.h:170,
                 from /__w/1/s/filters/src/pyramid.cpp:38:
/__w/1/s/common/include/pcl/common/distances.h:180:47: error: 'const struct pcl::RGB' has no member named 'y'
     float diff_x = p2.x - p1.x, diff_y = p2.y - p1.y, diff_z = p2.z - p1.z;
                                               ^
/__w/1/s/common/include/pcl/common/distances.h:180:47: error: 'const struct pcl::RGB' has no member named 'y'
/__w/1/s/common/include/pcl/common/distances.h:180:69: error: 'const struct pcl::RGB' has no member named 'z'
     float diff_x = p2.x - p1.x, diff_y = p2.y - p1.y, diff_z = p2.z - p1.z;
                                                                     ^
/__w/1/s/common/include/pcl/common/distances.h:180:69: error: 'const struct pcl::RGB' has no member named 'z'

Caused at L548 of pyramid.hpp due to squaredEuclideanDistance which needs the point type to have x,y,z for computing Euclidean distance.

Derived from a post by @kunaltyagi in https://github.com/PointCloudLibrary/pcl/pull/3841#issuecomment-610744388

Start in filters/include/pcl/filters/impl/pyramid.hpp around line 548 and inspect the squaredEuclideanDistance call used by Pyramid::compute(). Reproduce the filters build to confirm the RGB compilation failure, then verify that the selected distance handling supports RGB and that the filters target builds successfully.