path.bounds should return numbers even when input coordinates are strings

[Philippe Rivière]

d3.geoPath().bounds({type: "MultiPoint", coordinates: [["-32", "-20"], [32, 20]]})

returns [["-32", "-20"], [32, 20]]. I suggest we coerce the coordinates to numbers in

d3-geo/src/path/bounds.js

Line 21 in 078f46d

 function boundsPoint(x, y) { 

related observablehq/plot#1264