Add an active = NULL argument to st_coordinates.sfnetwork

[agila5]

Is your feature request related to a problem? Please describe.
I think st_coordinates may adopt the same shortcut as st_geometry or st_as_sf, i.e.

library(sf)
#> Linking to GEOS 3.9.1, GDAL 3.2.1, PROJ 7.2.1; sf_use_s2() is TRUE
library(sfnetworks)

sfc <- st_sfc(st_linestring(rbind(c(0, 0), c(1, 1), c(2, 2), c(3, 3))))
sfn <- as_sfnetwork(sfc)
st_geometry(sfn, "edges") # works
#> Geometry set for 1 feature 
#> Geometry type: LINESTRING
#> Dimension:     XY
#> Bounding box:  xmin: 0 ymin: 0 xmax: 3 ymax: 3
#> CRS:           NA
#> LINESTRING (0 0, 1 1, 2 2, 3 3)
st_coordinates(sfn, "edges") # doesn't work since st_coordinates always return the active table
#>   X Y
#> 1 0 0
#> 2 3 3

^{Created on 2022-06-26 by the reprex package (v2.0.1)}

Describe the solution you'd like
We could add an active = NULL argument such that a call like st_coordinates(sfn, "edges") returns the coordinates of the edges table.

Describe alternatives you've considered
We can just modify the active table, but also this addition shouldn't be really difficult. Moreover, IMO, it's surprising that the same pattern works only for st_geometry and sf_as_sf()

[luukvdmeer]

Added in v0.6.0. Also for st_bbox()