Add a Barbs element

[philippjfr]

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Since we have a VectorField element now it would be nice if we had a similar Barbs element. Cartopy and matplotlib already support drawing barbs and it shouldn't be too difficult to draw barbs using bokeh too.

Here's what barbs look like in cartopy:

[jbednar]

Sounds good. For clarity, it would be helpful to paste a screenshot or link to another plotting program's barb glyphs to show what functionality would be expected, more concretely.

[acrosby]

I am interested in visualizing points with barbs in addition to the vector field example above.

What might be involved in, or where to start, getting an implementation equivalent to MPL's (https://matplotlib.org/api/_as_gen/matplotlib.pyplot.barbs.html#matplotlib.pyplot.barbs) over to bokeh/geoviews?

Here's MPL's barb demo (https://matplotlib.org/gallery/images_contours_and_fields/barb_demo.html#sphx-glr-gallery-images-contours-and-fields-barb-demo-py):

[jbednar]

I've been wondering when someone would start asking for this! :-)

[dwr-psandhu]

@jbednar Given mpl's implementation of barbs doesn't this issue belong to holoviews? I read the previous discussion that closed holoviz/holoviews#3901 based on cartopy's implementation.