Rename `experimentalH3ToLocalIj`, etc.

[ajfriend]

Relating to:

• experimentalH3ToLocalIj
• experimentalLocalIjToH3
• h3ToLocalIj.c
• testH3ToLocalIj.c
• localIjToH3.c
• ...and a few other places

Possible changes:

• drop experimental from the name
• use cell instead of h3
• update filters

[dfellis]

Weren't they called "experimental" because we have issues crossing multiple icosahedron faces with the current algorithm, but that it could be possible to resolve? Did we find a solution?

[nrabinowitz]

To my knowledge we did not find a solution here - we have a solution for gridPathCells and gridDistance, which also rely on an unfolded planar coordinate approach, but not for these. I think the other reason to call these experimental was so that users would not rely on the output - the idea was that you'd get i,j coords that would be symmetrical with the two functions, but that later versions of H3 might change the origin, etc of these coords.