arrow

GH-38228: [R] Fence examples that need dataset with `examplesIf` (#38229)

### Rationale for this change

The minimal nightly build are failing with examples that won't run without the dataset feature

### What changes are included in this PR?

- Added `examplesIf` where needed
- Redocumented

### Are these changes tested?

Yes, by all R CMD check jobs

### Are there any user-facing changes?

No
* Closes: #38228

Authored-by: Dewey Dunnington <dewey@fishandwhistle.net>
Signed-off-by: Dewey Dunnington <dewey@voltrondata.com>