[R] Properly instantiate empty arrays of extension types in Table__from_schema

[asfimport]

The PR for ARROW-12105 introduces the function Table__from_schema which creates an empty Table from a Schema object. Currently it can't handle extension types, and instead just returns NULL type objects.

Reporter: Nicola Crane / @thisisnic
Assignee: Dewey Dunnington / @paleolimbot

Related issues:

• [R] Replace vars_select, vars_rename with eval_select, eval_rename (relates to)

PRs and other links:

• GitHub Pull Request #14519

_{Note: This issue was originally created as ARROW-18043. Please see the migration documentation for further details.}

[asfimport]

Nicola Crane / @thisisnic:
@paleolimbot Mind taking a look at this some time? It's not a priority for 10.0.0 though.

[asfimport]

Nicola Crane / @thisisnic:
Issue resolved by pull request 14519
#14519