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GH-38043: [R] Enable all features by default on macOS (#38195)

### Rationale for this change

Previously GCS/S3 support would need to be explicitly enabled in source builds (when they are build without `NOT_CRAN`). As we want the macos binaries to be fully featured we should turn the features on when the dependencies exists. 

### What changes are included in this PR?

This PR enables this behavior for macOS only, on Linux setting `NOT_CRAN` or  `LIBARROW_MINIMAL=false` is still required.

### Are these changes tested?

Crossbow and locally (thanks @ paleolimbot )
* Closes: #38043

Lead-authored-by: Jacob Wujciak-Jens <jacob@wujciak.de>
Co-authored-by: Dewey Dunnington <dewey@dunnington.ca>
Co-authored-by: Jonathan Keane <jkeane@gmail.com>
Signed-off-by: Jacob Wujciak-Jens <jacob@wujciak.de>