[SPARK-14798][SQL] Move native command and script transformation parsing into SparkSqlAstBuilder

[rxin]

What changes were proposed in this pull request?

This patch moves native command and script transformation into SparkSqlAstBuilder. This builds on #12561. See the last commit for diff.

How was this patch tested?

Updated test cases to reflect this.

[yhuai]

d813783 looks good

[SparkQA]

Test build #56497 has finished for PR 12564 at commit 5e99598.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #56506 has finished for PR 12564 at commit ecc9ea7.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #2840 has finished for PR 12564 at commit ecc9ea7.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #56557 has finished for PR 12564 at commit a38eaf1.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #56571 has finished for PR 12564 at commit 21b5397.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[SparkQA]

Test build #56576 has finished for PR 12564 at commit 81c9dbd.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
  • implicit class SchemaAttribute(f: CatalogColumn)

[SparkQA]

Test build #2849 has finished for PR 12564 at commit 21b5397.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds no public classes.

[yhuai]

LGTM

[SparkQA]

Test build #56587 has finished for PR 12564 at commit 1356aa0.

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

[rxin]

Merging in master.