### What changes were proposed in this pull request?
The RuntimeReplaceable ones are runtime replaceable, thus, their original parameters are not going to be resolved to PrettyAttribute and remain debug style string if we directly implement their `sql` methods with their parameters' `sql` methods.
This PR is raised with suggestions by maropu and cloud-fan https://github.com/apache/spark/pull/28402/files#r417656589. In this PR, we re-implement the `sql` methods of the RuntimeReplaceable ones with toPettySQL
### Why are the changes needed?
Consistency of schema output between RuntimeReplaceable expressions and normal ones.
For example, `date_format` vs `to_timestamp`, before this PR, they output differently
#### Before
```sql
select date_format(timestamp '2019-10-06', 'yyyy-MM-dd uuuu')
struct<date_format(TIMESTAMP '2019-10-06 00:00:00', yyyy-MM-dd uuuu):string>
select to_timestamp("2019-10-06S10:11:12.12345", "yyyy-MM-dd'S'HH:mm:ss.SSSSSS")
struct<to_timestamp('2019-10-06S10:11:12.12345', 'yyyy-MM-dd\'S\'HH:mm:ss.SSSSSS'):timestamp>
```
#### After
```sql
select date_format(timestamp '2019-10-06', 'yyyy-MM-dd uuuu')
struct<date_format(TIMESTAMP '2019-10-06 00:00:00', yyyy-MM-dd uuuu):string>
select to_timestamp("2019-10-06T10:11:12'12", "yyyy-MM-dd'T'HH:mm:ss''SSSS")
struct<to_timestamp(2019-10-06T10:11:12'12, yyyy-MM-dd'T'HH:mm:ss''SSSS):timestamp>
````
### Does this PR introduce _any_ user-facing change?
Yes, the schema output style changed for the runtime replaceable expressions as shown in the above example
### How was this patch tested?
regenerate all related tests
Closes#28420 from yaooqinn/SPARK-31615.
Authored-by: Kent Yao <yaooqinn@hotmail.com>
Signed-off-by: Takeshi Yamamuro <yamamuro@apache.org>
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