[SPARK-33281][SQL] Return SQL schema instead of Catalog string from the SchemaOfCsv expression

[MaxGekk]

What changes were proposed in this pull request?

Return schema in SQL format instead of Catalog string from the SchemaOfCsv expression.

Why are the changes needed?

To unify output of the schema_of_json() and schema_of_csv().

Does this PR introduce any user-facing change?

Yes, they can but schema_of_csv() is usually used in combination with from_csv(), so, the format of schema shouldn't be much matter.

Before:

> SELECT schema_of_csv('1,abc');
  struct<_c0:int,_c1:string>

After:

> SELECT schema_of_csv('1,abc');
  STRUCT<`_c0`: INT, `_c1`: STRING>

How was this patch tested?

By existing test suites CsvFunctionsSuite and CsvExpressionsSuite.

[SparkQA]

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[SparkQA]

Test build #130398 has finished for PR 30180 at commit cb1215a.

• This patch passes all tests.
• This patch merges cleanly.
• This patch adds no public classes.

[HyukjinKwon]

Merged to master.