[R] Support to collect decimal type

[asfimport]

Collecting from sparklyr decimal types through: 

devtools::install_github("apache/arrow", subdir = "r")
devtools::install_github("rstudio/sparklyr", ref = "feature/arrow")

library(sparklyr)
library(arrow)

sc <- spark_connect(master = "local")
sdf_len(sc, 3) %>% dplyr::mutate(new = 1) %>% dplyr::collect()

causes,

Error in RecordBatch__to_dataframe(x) : cannot handle Array of type decimal

Reporter: Javier Luraschi / @javierluraschi
Assignee: Javier Luraschi / @javierluraschi

PRs and other links:

• GitHub Pull Request #2819
• GitHub Pull Request #2876

_{Note: This issue was originally created as ARROW-3591. Please see the migration documentation for further details.}

[asfimport]

Kouhei Sutou / @kou:
Issue resolved by pull request 2819
#2819