### What changes were proposed in this pull request?
This pull request exposes the `make_interval` function, [as suggested here](https://github.com/apache/spark/pull/31000#pullrequestreview-560812433), and as agreed to [here](https://github.com/apache/spark/pull/31000#issuecomment-754856820) and [here](https://github.com/apache/spark/pull/31000#issuecomment-755040234).
This powerful little function allows for idiomatic datetime arithmetic via the Scala API:
```scala
// add two hours
df.withColumn("plus_2_hours", col("first_datetime") + make_interval(hours = lit(2)))
// subtract one week and 30 seconds
col("d") - make_interval(weeks = lit(1), secs = lit(30))
```
The `make_interval` [SQL function](https://github.com/apache/spark/pull/26446) already exists.
Here is [the JIRA ticket](https://issues.apache.org/jira/browse/SPARK-33995) for this PR.
### Why are the changes needed?
The Spark API makes it easy to perform datetime addition / subtraction with months (`add_months`) and days (`date_add`). Users need to write code like this to perform datetime addition with years, weeks, hours, minutes, or seconds:
```scala
df.withColumn("plus_2_hours", expr("first_datetime + INTERVAL 2 hours"))
```
We don't want to force users to manipulate SQL strings when they're using the Scala API.
### Does this PR introduce _any_ user-facing change?
Yes, this PR adds `make_interval` to the `org.apache.spark.sql.functions` API.
This single function will benefit a lot of users. It's a small increase in the surface of the API for a big gain.
### How was this patch tested?
This was tested via unit tests.
cc: MaxGekk
Closes#31073 from MrPowers/SPARK-33995.
Authored-by: MrPowers <matthewkevinpowers@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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