[SPARK-19130][SPARKR] Support setting literal value as column implicitly

## What changes were proposed in this pull request?

```
df$foo <- 1
```

instead of
```
df$foo <- lit(1)
```

## How was this patch tested?

unit tests

Author: Felix Cheung <felixcheung_m@hotmail.com>

Closes #16510 from felixcheung/rlitcol.