Update docs to use {sf} or {terra}

[schloerke]

With the archival of legacy spatial packages, sf and terra are the new "best practices" packages. sp is still there, but uses sf under the hood https://r-spatial.org/r/2023/04/10/evolution3.html

Originally posted by @olivroy in #903 (comment)

[jack-davison]

Related (though perhaps a different issue?) - is there intention to export the example data (e.g., https://rstudio.github.io/leaflet/reference/breweries91.html) as {sf} dataframes/tibbles rather than sp::SpatialPointsDataFrames?

When teaching others {leaflet}/spatial data analysis it's handy to have that example spatial data, but you're suddenly then explaining what a SpatialPointsDataFrame is and why it's different from the sf dataframe we've already used!