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ARROW-17620: [R] as_arrow_array() ignores type for StructArrays (#14047)

As described in https://issues.apache.org/jira/browse/ARROW-17620, `as_arrow_array()` ignores user-provided types passed by the `type` argument.

This PR explicitly adds the `type` name argument to the `Map` call. Currently, the argument gets passed to the ellipsis and gets ignored.

I also added a test. Let me know if there is a better place for it (or a better test).

Lead-authored-by: François Michonneau <francois.michonneau@gmail.com>
Co-authored-by: Nic Crane <thisisnic@gmail.com>
Signed-off-by: Nic Crane <thisisnic@gmail.com>