Add support to facilitate locating quivers on triangle meshes

[erogluorhan]

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Proposed new feature or change:

_Originally posted by @clyne in https://github.com/NCAR/geocat-viz/issues/24#issue-678827365 :

When generating 2D hedgehog (quiver) plots users typically want to locate quiver glyphs on at 2D lattice. The MPL quiver function operates on a list of 2D vectors specified along with their coordinates. Thus for regular grids it is easy to locate quivers along a lattice simply by locating them at grid nodes. For unstructured data locating the quivers at grid nodes will not result in a regular placement of glyph locations. To support placing quivers at regular intervals the unstructured mesh needs to be sampled at arbitrary locations. This feature request is for a mechanism to sample an MPL triangle mesh such that at regularized list of vectors and their coordinates can be generated and fed into the MPL quiver function.