"Populate mesh" node mk2

[portnov]

Refs #4434.
This introduces a new implementation of "Populate mesh" node, which should have all features of old "populate mesh" as well as many features of "populate solid" node.
This version may be a little slower than previous, but given the amount of features I believe this is acceptable.

• ability to generate points inside mesh, on mesh surface or on mesh edges
• ability to specify points distribution by scalar field
• ability to control number of points per face / edge either proportionally to face area / edge length, and by manually specifying weights;
• weights can be used as mask per face / per edge
• ability to control distance between nearest points as minimum distance value, or by providing scalar field specifying free space radius around each point

Preflight checklist

Put an x letter in each brackets when you're done this item:

• Code changes complete.
• Code documentation complete.
• Documentation for users complete (or not required, if user never sees these changes).
• Manual testing done.
• Unit-tests implemented.
• Ready for merge.