[SPARK-12841][SQL][branch-1.6] fix cast in filter

[cloud-fan]

In SPARK-10743 we wrap cast with UnresolvedAlias to give Cast a better alias if possible. However, for cases like filter, the UnresolvedAlias can't be resolved and actually we don't need a better alias for this case. This PR move the cast wrapping logic to Column.named so that we will only do it when we need a alias name.

backport #10781 to 1.6

[cloud-fan]

cc @yhuai

[rxin]

Can you update the pull request description to include more information? The old pull request description is good.

[SparkQA]

Test build #49633 has finished for PR 10819 at commit 4e3269b.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[cloud-fan]

retest this please

[SparkQA]

Test build #49635 has finished for PR 10819 at commit 4e3269b.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[yhuai]

test this please

[SparkQA]

Test build #49638 has finished for PR 10819 at commit 4e3269b.

• This patch fails to build.
• This patch merges cleanly.
• This patch adds no public classes.

[cloud-fan]

something wrong with branch 1.6? cc @JoshRosen

[JoshRosen]

There might be something wrong with that build workspace's Ivy cache. If you have Jenkins access, you should be able to SSH in and wipe it away.

[cloud-fan]

retest this please

[SparkQA]

Test build #49655 has finished for PR 10819 at commit 4e3269b.

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

[yhuai]

Thanks! Merging to branch 1.6.

[rxin]

@cloud-fan you'd need to close this pull request yourself since it was not merged into master.