[SPARK-28123][SQL] String Functions: support btrim

[beliefer]

What changes were proposed in this pull request?

The current implement of Trim/Ltrim/Rtrim only support string, but support byte array is very useful.
The function btrim supports byte array.

The mainstream database support this feature show below:

Postgresql
https://www.postgresql.org/docs/11/functions-binarystring.html

Vertica
https://www.vertica.com/docs/9.2.x/HTML/Content/Authoring/SQLReferenceManual/Functions/String/BTRIM.htm?tocpath=SQL%20Reference%20Manual%7CSQL%20Functions%7CString%20Functions%7C_____5

Redshift
https://docs.aws.amazon.com/redshift/latest/dg/r_BTRIM.html

Druid
https://druid.apache.org/docs/latest/querying/sql.html#string-functions

Greenplum
http://docs.greenplum.org/6-8/ref_guide/function-summary.html

Why are the changes needed?

btrim is very useful.

Does this PR introduce any user-facing change?

Yes. btrim is a new function

How was this patch tested?

Jenkins test.

[SparkQA]

Test build #133780 has finished for PR 31080 at commit 179292f.

• This patch fails Spark unit tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
• case class BinaryTrim(srcBinary: Expression, trimBinary: Option[Expression] = None)

[beliefer]

retest this please

[SparkQA]

Kubernetes integration test starting
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/38379/

[SparkQA]

Kubernetes integration test status success
URL: https://amplab.cs.berkeley.edu/jenkins/job/SparkPullRequestBuilder-K8s/38379/

[SparkQA]

Test build #133790 has finished for PR 31080 at commit 179292f.

• This patch fails SparkR unit tests.
• This patch merges cleanly.
• This patch adds the following public classes (experimental):
• case class BinaryTrim(srcBinary: Expression, trimBinary: Option[Expression] = None)

[beliefer]

retest this please

[SparkQA]

Test build #133801 has started for PR 31080 at commit 179292f.

[beliefer]

cc @cloud-fan

[srowen]

Per the other PR/JIRA discussion, I'm still skeptical about the use case for this function. IF it's just that legacy DBs support it, it may not be worth it just for that reason.