## What changes were proposed in this pull request?

This PR proposes to deprecate `register*` for UDFs in `SQLContext` and `Catalog` in Spark 2.3.0.

These are inconsistent with Scala / Java APIs and also these basically do the same things with `spark.udf.register*`.

Also, this PR moves the logcis from `[sqlContext|spark.catalog].register*` to `spark.udf.register*` and reuse the docstring.

This PR also handles minor doc corrections. It also includes https://github.com/apache/spark/pull/20158

## How was this patch tested?

Manually tested, manually checked the API documentation and tests added to check if deprecated APIs call the aliases correctly.

Author: hyukjinkwon <gurwls223@gmail.com>

Closes #20288 from HyukjinKwon/deprecate-udf.