Add lightmap texcoord set field

[iche033]

needed by gazebosim/gz-sim#471

the light_map field was recently added but we also need to specify the texture coordinate set for the lightmap.

Signed-off-by: Ian Chen [email protected]

[codecov]

Codecov Report

Merging #124 (2686fc5) into main (668a75b) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #124   +/-   ##
=======================================
  Coverage   84.59%   84.59%           
=======================================
  Files           7        7           
  Lines         818      818           
=======================================
  Hits          692      692           
  Misses        126      126           

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[chapulina]

Merging now so it gets into the nightly build.