## What changes were proposed in this pull request?
In the PR, I propose to deprecate the `from_utc_timestamp()` and `to_utc_timestamp`, and disable them by default. The functions can be enabled back via the SQL config `spark.sql.legacy.utcTimestampFunc.enabled`. By default, any calls of the functions throw an analysis exception.
One of the reason for deprecation is functions violate semantic of `TimestampType` which is number of microseconds since epoch in UTC time zone. Shifting microseconds since epoch by time zone offset doesn't make sense because the result doesn't represent microseconds since epoch in UTC time zone any more, and cannot be considered as `TimestampType`.
## How was this patch tested?
The changes were tested by `DateExpressionsSuite` and `DateFunctionsSuite`.
Closes#24195 from MaxGekk/conv-utc-timestamp-deprecate.
Lead-authored-by: Maxim Gekk <max.gekk@gmail.com>
Co-authored-by: Maxim Gekk <maxim.gekk@databricks.com>
Co-authored-by: Hyukjin Kwon <gurwls223@apache.org>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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