common case helper for texture UVs added

[EgeCiklabakkal]

[nmwsharp]

Hi, thanks for opening this pull request!

I totally support the adding these UV common-case helpers, but I think a few changes might be needed compared with this strategy.

• If there are no UV properties, we should throw an error. This might not be the best behavior, but it should be consistent with other functions like getVertexColor()
• All-zero UVs probably shouldn't get special treatment in the library, that can be handled in the user's application
• We should probably check a few common names for UV's, I've seen s and t as well for instance.

[fire]

Is this pr salvageable? Can you propose tasks?