[SPARK-15463][SQL] Add an API to load DataFrame from Dataset[String] storing CSV

## What changes were proposed in this pull request?

This PR proposes to add an API that loads `DataFrame` from `Dataset[String]` storing csv.

It allows pre-processing before loading into CSV, which means allowing a lot of workarounds for many narrow cases, for example, as below:

- Case 1 - pre-processing

  ```scala
  val df = spark.read.text("...")
  // Pre-processing with this.
  spark.read.csv(df.as[String])
  ```

- Case 2 - use other input formats

  ```scala
  val rdd = spark.sparkContext.newAPIHadoopFile("/file.csv.lzo",
    classOf[com.hadoop.mapreduce.LzoTextInputFormat],
    classOf[org.apache.hadoop.io.LongWritable],
    classOf[org.apache.hadoop.io.Text])
  val stringRdd = rdd.map(pair => new String(pair._2.getBytes, 0, pair._2.getLength))

  spark.read.csv(stringRdd.toDS)
  ```

## How was this patch tested?

Added tests in `CSVSuite` and build with Scala 2.10.

```
./dev/change-scala-version.sh 2.10
./build/mvn -Pyarn -Phadoop-2.4 -Dscala-2.10 -DskipTests clean package
```

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #16854 from HyukjinKwon/SPARK-15463.