### What changes were proposed in this pull request?
In the PR, I propose:
1. To replace matching by `Literal` in `ExprUtils.evalSchemaExpr()` to checking foldable property of the `schema` expression.
2. To replace matching by `Literal` in `ExprUtils.evalTypeExpr()` to checking foldable property of the `schema` expression.
3. To change checking of the input parameter in the `SchemaOfCsv` expression, and allow foldable `child` expression.
4. To change checking of the input parameter in the `SchemaOfJson` expression, and allow foldable `child` expression.
### Why are the changes needed?
This should improve Spark SQL UX for `from_csv`/`from_json`. Currently, Spark expects only literals:
```sql
spark-sql> select from_csv('1,Moscow', replace('dpt_org_id INT, dpt_org_city STRING', 'dpt_org_', ''));
Error in query: Schema should be specified in DDL format as a string literal or output of the schema_of_csv function instead of replace('dpt_org_id INT, dpt_org_city STRING', 'dpt_org_', '');; line 1 pos 7
spark-sql> select from_json('{"id":1, "city":"Moscow"}', replace('dpt_org_id INT, dpt_org_city STRING', 'dpt_org_', ''));
Error in query: Schema should be specified in DDL format as a string literal or output of the schema_of_json function instead of replace('dpt_org_id INT, dpt_org_city STRING', 'dpt_org_', '');; line 1 pos 7
```
and only string literals are acceptable as CSV examples by `schema_of_csv`/`schema_of_json`:
```sql
spark-sql> select schema_of_csv(concat_ws(',', 0.1, 1));
Error in query: cannot resolve 'schema_of_csv(concat_ws(',', CAST(0.1BD AS STRING), CAST(1 AS STRING)))' due to data type mismatch: The input csv should be a string literal and not null; however, got concat_ws(',', CAST(0.1BD AS STRING), CAST(1 AS STRING)).; line 1 pos 7;
'Project [unresolvedalias(schema_of_csv(concat_ws(,, cast(0.1 as string), cast(1 as string))), None)]
+- OneRowRelation
spark-sql> select schema_of_json(regexp_replace('{"item_id": 1, "item_price": 0.1}', 'item_', ''));
Error in query: cannot resolve 'schema_of_json(regexp_replace('{"item_id": 1, "item_price": 0.1}', 'item_', ''))' due to data type mismatch: The input json should be a string literal and not null; however, got regexp_replace('{"item_id": 1, "item_price": 0.1}', 'item_', '').; line 1 pos 7;
'Project [unresolvedalias(schema_of_json(regexp_replace({"item_id": 1, "item_price": 0.1}, item_, )), None)]
+- OneRowRelation
```
### Does this PR introduce any user-facing change?
Yes, after the changes users can pass any foldable string expression as the `schema` parameter to `from_csv()/from_json()`. For the example above:
```sql
spark-sql> select from_csv('1,Moscow', replace('dpt_org_id INT, dpt_org_city STRING', 'dpt_org_', ''));
{"id":1,"city":"Moscow"}
spark-sql> select from_json('{"id":1, "city":"Moscow"}', replace('dpt_org_id INT, dpt_org_city STRING', 'dpt_org_', ''));
{"id":1,"city":"Moscow"}
```
After change the `schema_of_csv`/`schema_of_json` functions accept foldable expressions, for example:
```sql
spark-sql> select schema_of_csv(concat_ws(',', 0.1, 1));
struct<_c0:double,_c1:int>
spark-sql> select schema_of_json(regexp_replace('{"item_id": 1, "item_price": 0.1}', 'item_', ''));
struct<id:bigint,price:double>
```
### How was this patch tested?
Added new test to `CsvFunctionsSuite` and to `JsonFunctionsSuite`.
Closes#27804 from MaxGekk/foldable-arg-csv-json-func.
Authored-by: Maxim Gekk <max.gekk@gmail.com>
Signed-off-by: Wenchen Fan <wenchen@databricks.com>
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