Optimization in getEdgeHexagons

[heshpdx]

Replace 4 fpdiv's with 1 fpdiv and 4 fpmul's.

I ran benchmarkPolygonToCellsExperimental and benchmarkPolygonToCells on my Ampere Altra, and here are the results. The Alameda geoloop is doing well at +5.5%.

benchmark	old	new	ratio
polygonToCellsSF_Center	1651.815	1644.885	1.0042
polygonToCellsSF_Full	4763.64	4729.577	1.0072
polygonToCellsSF_Overlapping	5672.139	5646.54	1.0045
polygonToCellsAlameda_Center	3889.226	3686.52	1.0550
polygonToCellsAlameda_Full	9900.065	9650.448	1.0259
polygonToCellsAlameda_Overlapping	12840.43	12585.24	1.0203
polygonToCellsSouthernExpansion_Center	76209.64	76028.62	1.0024
polygonToCellsSouthernExpansion_Full	228112.8	226663.6	1.0064
polygonToCellsSouthernExpansion_Overlapping	370727.4	367403.3	1.0090
polygonToCellsSF	2804.544	2803.674	1.0003
polygonToCellsAlameda	4218.331	4215.235	1.0007
polygonToCellsSouthernExpansion	125736.6	125077.6	1.0053

[coveralls]

coverage: 98.825% (+0.001%) from 98.824%
when pulling 9a157d8 on heshpdx:hex_algo
into 4899d29 on uber:master.

[heshpdx]

Thank you! Also if you didn't see, Uber moved their services to Ampere servers in OCI cloud:
https://www.cio.com/article/3513933/uber-embraces-the-cloud-with-customized-cpus.html