[SPARK-14321][SQL] Reduce date format cost and string-to-date cost in date functions

## What changes were proposed in this pull request?
The current implementations of `UnixTime` and `FromUnixTime` do not cache their parser/formatter as much as they could. This PR resolved this issue.

This PR is a take over from https://github.com/apache/spark/pull/13522 and further optimizes the re-use of the parser/formatter. It also fixes the improves handling (catching the actual exception instead of `Throwable`). All credits for this work should go to rajeshbalamohan.

This PR closes https://github.com/apache/spark/pull/13522

## How was this patch tested?
Current tests.

Author: Herman van Hovell <hvanhovell@databricks.com>
Author: Rajesh Balamohan <rbalamohan@apache.org>

Closes #13581 from hvanhovell/SPARK-14321.