[SPARK-15318][ML][EXAMPLE] spark.ml Collaborative Filtering example does not work in spark-shell

## What changes were proposed in this pull request?

(Please fill in changes proposed in this fix)

copy & paste example in ml-collaborative-filtering.html into spark-shell, we see the following errors.
scala> case class Rating(userId: Int, movieId: Int, rating: Float, timestamp: Long)
defined class Rating

scala> object Rating {
def parseRating(str: String): Rating = { | val fields = str.split("::") | assert(fields.size == 4) | Rating(fields(0).toInt, fields(1).toInt, fields(2).toFloat, fields(3).toLong) | }
}
<console>:29: error: Rating.type does not take parameters
Rating(fields(0).toInt, fields(1).toInt, fields(2).toFloat, fields(3).toLong)
^
In standard scala repl, it has the same error.

Scala/spark-shell repl has some quirks (e.g. packages are also not well supported).

The reason of errors is that scala/spark-shell repl discards previous definitions when we define the Object with the same class name. Solution: We can rename the Object Rating.

## How was this patch tested?

(Please explain how this patch was tested. E.g. unit tests, integration tests, manual tests)

Manually test it: 1). ./bin/run-example ALSExample
2). copy & paste example in the generated document. It works fine.

Author: wm624@hotmail.com <wm624@hotmail.com>

Closes #13110 from wangmiao1981/repl.

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