[R] Improve efficiency of schema creation to prevent performance regressions

[asfimport]

In ARROW-12105 the functionality implemented introduced some performance regressions that we should sort out before the release.

Reporter: Nicola Crane / @thisisnic
Assignee: Nicola Crane / @thisisnic

PRs and other links:

• GitHub Pull Request #14447

_{Note: This issue was originally created as ARROW-18079. Please see the migration documentation for further details.}

[asfimport]

Kouhei Sutou / @kou:
If we may need to take a long time to fix this, can we revert ARROW-12105 for 10.0.0?

[asfimport]

Nicola Crane / @thisisnic:
I was planning to take a look at it tomorrow, if that's not too late?

[asfimport]

Kouhei Sutou / @kou:
OK. That's not too late. Because we still have some blockers: https://cwiki.apache.org/confluence/display/ARROW/Arrow+10.0.0+Release

[asfimport]

Nicola Crane / @thisisnic:
Great! Ping me again if this one does become the last blocker, and then, sure, we can revert ARROW-12105 if we need to, but I'm gonna see what I can do to try to not need to.

[asfimport]

Nicola Crane / @thisisnic:
Issue resolved by pull request 14447
#14447