### What changes were proposed in this pull request?
Return schema in SQL format instead of Catalog string from the `SchemaOfJson` expression.
### Why are the changes needed?
In some cases, `from_json()` cannot parse schemas returned by `schema_of_json`, for instance, when JSON fields have spaces (gaps). Such fields will be quoted after the changes, and can be parsed by `from_json()`.
Here is the example:
```scala
val in = Seq("""{"a b": 1}""").toDS()
in.select(from_json('value, schema_of_json("""{"a b": 100}""")) as "parsed")
```
raises the exception:
```
== SQL ==
struct<a b:bigint>
------^^^
at org.apache.spark.sql.catalyst.parser.ParseException.withCommand(ParseDriver.scala:263)
at org.apache.spark.sql.catalyst.parser.AbstractSqlParser.parse(ParseDriver.scala:130)
at org.apache.spark.sql.catalyst.parser.AbstractSqlParser.parseTableSchema(ParseDriver.scala:76)
at org.apache.spark.sql.types.DataType$.fromDDL(DataType.scala:131)
at org.apache.spark.sql.catalyst.expressions.ExprUtils$.evalTypeExpr(ExprUtils.scala:33)
at org.apache.spark.sql.catalyst.expressions.JsonToStructs.<init>(jsonExpressions.scala:537)
at org.apache.spark.sql.functions$.from_json(functions.scala:4141)
```
### Does this PR introduce _any_ user-facing change?
Yes. For example, `schema_of_json` for the input `{"col":0}`.
Before: `struct<col:bigint>`
After: `STRUCT<`col`: BIGINT>`
### How was this patch tested?
By existing test suites `JsonFunctionsSuite` and `JsonExpressionsSuite`.
Closes#30172 from MaxGekk/schema_of_json-sql-schema.
Authored-by: Max Gekk <max.gekk@gmail.com>
Signed-off-by: HyukjinKwon <gurwls223@apache.org>
9d5e48ea95