[SPARK-51468][SQL] Revert "From json/xml should not change collations in the given schema"

### What changes were proposed in this pull request?
After removing session-level collation (#49772) we can also revert the PR that changed the behavior of `from_json` and `from_xml` expressions to use json and not sql type representation under the hood (#48750).

### Why are the changes needed?
Now that we don't have correctness problems with session level collation, using `sql` instead of `json` will lead to smaller and more efficient type representation.

### Does this PR introduce _any_ user-facing change?
No.

### How was this patch tested?
Existing unit tests.

### Was this patch authored or co-authored using generative AI tooling?
No.

Closes #50234 from stefankandic/revertFromJsonChange.

Authored-by: Stefan Kandic <stefan.kandic@databricks.com>
Signed-off-by: Max Gekk <max.gekk@gmail.com>
(cherry picked from commit 0094f44)
Signed-off-by: Max Gekk <max.gekk@gmail.com>

Author: stefankandic

sql/api/src/main/scala/org/apache/spark/sql/functions.scala

@@ -6901,7 +6901,7 @@ object functions {
    */
   // scalastyle:on line.size.limit
   def from_json(e: Column, schema: DataType, options: Map[String, String]): Column = {
-    from_json(e, lit(schema.json), options.iterator)
+    from_json(e, lit(schema.sql), options.iterator)
   }
 
   // scalastyle:off line.size.limit
@@ -7773,7 +7773,7 @@ object functions {
    */
   // scalastyle:on line.size.limit
   def from_xml(e: Column, schema: StructType, options: java.util.Map[String, String]): Column =
-    from_xml(e, lit(schema.json), options.asScala.iterator)
+    from_xml(e, lit(schema.sql), options.asScala.iterator)
 
   // scalastyle:off line.size.limit
   /**

sql/connect/common/src/test/resources/query-tests/queries/function_from_json.json

@@ -37,7 +37,7 @@
           }
         }, {
           "literal": {
-            "string": "{\"type\":\"struct\",\"fields\":[{\"name\":\"id\",\"type\":\"long\",\"nullable\":true,\"metadata\":{}},{\"name\":\"a\",\"type\":\"integer\",\"nullable\":true,\"metadata\":{}},{\"name\":\"b\",\"type\":\"double\",\"nullable\":true,\"metadata\":{}}]}"
+            "string": "STRUCT\u003cid: BIGINT, a: INT, b: DOUBLE\u003e"
           },
           "common": {
             "origin": {

sql/connect/common/src/test/resources/query-tests/queries/function_from_json.proto.bin

@@ -37,7 +37,7 @@
           }
         }, {
           "literal": {
-            "string": "{\"type\":\"struct\",\"fields\":[{\"name\":\"id\",\"type\":\"long\",\"nullable\":true,\"metadata\":{}},{\"name\":\"a\",\"type\":\"integer\",\"nullable\":true,\"metadata\":{}},{\"name\":\"b\",\"type\":\"double\",\"nullable\":true,\"metadata\":{}}]}"
+            "string": "STRUCT\u003cid: BIGINT, a: INT, b: DOUBLE\u003e"
           },
           "common": {
             "origin": {