[SPARK-9871] [SPARKR] Add expression functions into SparkR which have a variable parameter

### Summary

- Add `lit` function
- Add `concat`, `greatest`, `least` functions

I think we need to improve `collect` function in order to implement `struct` function. Since `collect` doesn't work with arguments which includes a nested `list` variable. It seems that a list against `struct` still has `jobj` classes. So it would be better to solve this problem on another issue.

### JIRA
[[SPARK-9871] Add expression functions into SparkR which have a variable parameter - ASF JIRA](https://issues.apache.org/jira/browse/SPARK-9871)

Author: Yu ISHIKAWA <yuu.ishikawa@gmail.com>

Closes #8194 from yu-iskw/SPARK-9856.