### What changes were proposed in this pull request?
When input column lengths can not be inferred and handleInvalid = "keep", VectorAssembler will throw a runtime exception. However the error message with this exception is not consistent. I change the content of this error message to make it work properly.
### Why are the changes needed?
This is a bug. Here is a simple example to reproduce it.
```
// create a df without vector size
val df = Seq(
(Vectors.dense(1.0), Vectors.dense(2.0))
).toDF("n1", "n2")
// only set vector size hint for n1 column
val hintedDf = new VectorSizeHint()
.setInputCol("n1")
.setSize(1)
.transform(df)
// assemble n1, n2
val output = new VectorAssembler()
.setInputCols(Array("n1", "n2"))
.setOutputCol("features")
.setHandleInvalid("keep")
.transform(hintedDf)
// because only n1 has vector size, the error message should tell us to set vector size for n2 too
output.show()
```
Expected error message:
```
Can not infer column lengths with handleInvalid = "keep". Consider using VectorSizeHint to add metadata for columns: [n2].
```
Actual error message:
```
Can not infer column lengths with handleInvalid = "keep". Consider using VectorSizeHint to add metadata for columns: [n1, n2].
```
This introduce difficulties when I try to resolve this exception, for I do not know which column required vectorSizeHint. This is especially troublesome when you have a large number of columns to deal with.
### Does this PR introduce _any_ user-facing change?
No.
### How was this patch tested?
Add test in VectorAssemblerSuite.
Closes#28487 from fan31415/SPARK-31671.
Lead-authored-by: fan31415 <fan12356789@gmail.com>
Co-authored-by: yijiefan <fanyije@gmail.com>
Signed-off-by: Sean Owen <srowen@gmail.com>
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