[R] altrep vectors from Array with nulls

[asfimport]

Reporter: Romain Francois / @romainfrancois
Assignee: Romain Francois / @romainfrancois

PRs and other links:

• GitHub Pull Request #10730

_{Note: This issue was originally created as ARROW-13164. Please see the migration documentation for further details.}

[asfimport]

Neal Richardson / @nealrichardson:
Issue resolved by pull request 10730
#10730