[SPARK-5167][SQL] Move Row into sql package and make it usable for Java.

[rxin]

Mostly just moving stuff around. This should still be source compatible since we type aliased Row previously in org.apache.spark.sql.Row.

Added the following APIs to Row:

def getMap[K, V](i: Int): scala.collection.Map[K, V]
def getJavaMap[K, V](i: Int): java.util.Map[K, V]
def getSeq[T](i: Int): Seq[T]
def getList[T](i: Int): java.util.List[T]
def getStruct(i: Int): StructType

[SparkQA]

Test build #25496 has started for PR 4030 at commit 82b064a.

• This patch merges cleanly.

[SparkQA]

Test build #25496 has finished for PR 4030 at commit 82b064a.

• This patch fails Scala style tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test FAILed.
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Test FAILed.

[SparkQA]

Test build #25518 has started for PR 4030 at commit 6c85c29.

• This patch merges cleanly.

[SparkQA]

Test build #25518 has finished for PR 4030 at commit 6c85c29.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[AmplabJenkins]

Test PASSed.
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Test PASSed.

[rxin]

Merging in master.