### What changes were proposed in this pull request?
This PR proposes to:
1. Fix the error message when the output schema is misbatched with R DataFrame from the given function. For example,
```R
df <- createDataFrame(list(list(a=1L, b="2")))
count(gapply(df, "a", function(key, group) { group }, structType("a int, b int")))
```
**Before:**
```
Error in handleErrors(returnStatus, conn) :
...
java.lang.UnsupportedOperationException
...
```
**After:**
```
Error in handleErrors(returnStatus, conn) :
...
java.lang.AssertionError: assertion failed: Invalid schema from gapply: expected IntegerType, IntegerType, got IntegerType, StringType
...
```
2. Update documentation about the schema matching for `gapply` and `dapply`.
### Why are the changes needed?
To show which schema is not matched, and let users know what's going on.
### Does this PR introduce _any_ user-facing change?
Yes, error message is updated as above, and documentation is updated.
### How was this patch tested?
Manually tested and unitttests were added.
Closes#29283 from HyukjinKwon/r-vectorized-error.
Authored-by: HyukjinKwon <gurwls223@apache.org>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
e1d7321034