arrow

ARROW-17699: [R] Add better error message for if a non-schema passed into open_dataset() (#14108)

Example below shows what happens if the `schema()` function is passed in as the `schema` argument via the `...` argument to `open_dataset()`.

Before (a later check for something else catches it, this giving a misleading message):

```
library(dplyr)
library(arrow)
tf <- tempfile()
dir.create(tf)
write_dataset(mtcars, tf, format = "csv")
open_dataset(tf, format = "csv", schema = schema) %>% collect()
#> Error in `CsvFileFormat$create()`:
#> ! Values in `column_names` must match `schema` field names
#> ✖ `column_names` and `schema` field names match but are not in the same order
```

After (more accurate error message): 

```
library(dplyr)
library(arrow)
tf <- tempfile()
dir.create(tf)
write_dataset(mtcars, tf, format = "csv")
open_dataset(tf, format = "csv", schema = schema) %>% collect()
#> Error in `CsvFileFormat$create()`:
#> ! `schema` must be an object of class 'Schema' not 'function'.
```

Authored-by: Nic Crane <thisisnic@gmail.com>
Signed-off-by: Nic Crane <thisisnic@gmail.com>