[r] Replace tiledb-r with libtiledbsoma in the R API (parent task)

[johnkerl]

This is a sibling of #1632. Its sole job is to link-track, at the GitHub Issues level, smaller issues which will be split out as individual GitHub Issues.

Some sequencings:

• [r] Push schema accessor down to libtiledbsoma #3079 is the last spot R/TileDBArray.R needs the .tiledb_array / self$object TileDB-R array handle
• That in turn (as narrated on that PR) is blocked by [r] Use libtiledbsoma for schema evolution #3057
• Once 3057 and 3079 are merged then we can do [r] Use libtiledbsoma handles for arrays #3059
• Then [r] Use libtiledbsoma for the mode accessor #3060
• [r] Port QueryCondition from tiledb-r to tiledbsoma-r [WIP] #3083 appears somewhat orthogonal to that list just now
• Likewise [r] Use libtiledbsoma for schema/filter specification #3056