arrow

ARROW-17460: [R] Don't warn if the new UDF I'm registering is the same as the existing one (#14436)

This PR makes it so that you can do the following without a warning:

``` r
library(arrow, warn.conflicts = FALSE)

register_scalar_function(
  "times_32",
  function(context, x) x * 32L,
  in_type = list(int32(), int64(), float64()),
  out_type = function(in_types) in_types[[1]],
  auto_convert = TRUE
)

register_scalar_function(
  "times_32",
  function(context, x) x * 32L,
  in_type = list(int32(), int64(), float64()),
  out_type = function(in_types) in_types[[1]],
  auto_convert = TRUE
)
```

In fixing that, I also ran across an important discovery, which is that `cpp11::function` does *not* protect the underlying `SEXP` from garbage collection!!!! It the two functions we used this for were being protected by proxy because the execution environment of `register_scalar_function()` was being saved when the binding was registered.

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