Add ability to extract value at given map coordinates

[metasim]

Context:

https://gitter.im/locationtech/rasterframes?at=5eab3de75cd4fe50a3e0910c

Workaround:

https://gist.github.com/metasim/8b692afc8ee5da515f14f0c9e16ffd73

[BKDaugherty]

Hey @metasim! Is this something you still think should be added to rasterframes? I found myself wanting today to do something similar to what the user in the linked context was hoping to do, and am curious if the status of this has changed at all since then.

[metasim]

@BKDaugherty Yes, I think it should be a core capability :). PRs welcome!