[R] bindings for strptime

[asfimport]

Reporter: Neal Richardson / @nealrichardson
Assignee: Alenka Frim / @AlenkaF
Watchers: Rok Mihevc / @rok

PRs and other links:

• GitHub Pull Request #10334

_{Note: This issue was originally created as ARROW-12198. Please see the migration documentation for further details.}

[asfimport]

Alenka Frim / @AlenkaF:
I would like to have a go at this issue pls.

[asfimport]

Jonathan Keane / @jonkeane:
We always appreciate contributions, welcome! We've assigned the ticket to you (though that's a formality at most).

Let us know if you have any questions, or would like pointers / links to previous PRs that implemented similar bindings.

[asfimport]

Alenka Frim / @AlenkaF:
Thank you @jonkeane! 

I'm working on it and will let u know if I have any questions.

[asfimport]

Jonathan Keane / @jonkeane:
Issue resolved by pull request 10334
#10334